Program: 34036
Project: 34036
Buggy source:
@EventHandler(priority=EventPriority.LOWEST,ignoreCancelled=true) public void onPlayerMove(PlayerMoveEvent e){
  final Player player=e.getPlayer();
  if (player.isDead()) {
    return;
  }
  if (!player.getWorld().getName().equalsIgnoreCase(Settings.worldName)) {
    return;
  }
  if (player.isOp()) {
    if (!Settings.damageOps) {
      return;
    }
  }
 else   if (VaultHelper.checkPerm(player,Settings.PERMPREFIX + "String_Node_Str") || VaultHelper.checkPerm(player,Settings.PERMPREFIX + "String_Node_Str")) {
    return;
  }
  if (player.getGameMode().equals(GameMode.CREATIVE)) {
    return;
  }
  final Location playerLoc=player.getLocation();
  final Block block=playerLoc.getBlock();
  if (Settings.rainDamage > 0D && isRaining) {
    Biome biome=playerLoc.getBlock().getBiome();
    if (biome != Biome.DESERT && biome != Biome.DESERT_HILLS && biome != Biome.DESERT_MOUNTAINS && biome != Biome.SAVANNA && biome != Biome.SAVANNA_MOUNTAINS && biome != Biome.SAVANNA_PLATEAU && biome != Biome.SAVANNA_PLATEAU_MOUNTAINS && biome != Biome.MESA && biome != Biome.MESA_BRYCE && biome != Biome.MESA_PLATEAU && biome != Biome.MESA_PLATEAU_FOREST && biome != Biome.MESA_PLATEAU_FOREST_MOUNTAINS && biome != Biome.MESA_PLATEAU_MOUNTAINS && biome != Biome.HELL) {
      boolean hitByRain=true;
      for (int y=playerLoc.getBlockY() + 2; y < playerLoc.getWorld().getMaxHeight(); y++) {
        if (!playerLoc.getWorld().getBlockAt(playerLoc.getBlockX(),y,playerLoc.getBlockZ()).getType().equals(Material.AIR)) {
          hitByRain=false;
          break;
        }
      }
      if (!hitByRain) {
        wetPlayers.remove(player);
      }
 else {
        boolean acidPotion=false;
        Collection<PotionEffect> activePotions=player.getActivePotionEffects();
        for (        PotionEffect s : activePotions) {
          if (s.getType().equals(PotionEffectType.WATER_BREATHING)) {
            acidPotion=true;
          }
        }
        if (acidPotion) {
          wetPlayers.remove(player);
        }
 else {
          if (!wetPlayers.contains(player)) {
            wetPlayers.add(player);
            new BukkitRunnable(){
              @Override public void run(){
                if (!isRaining || player.isDead()) {
                  wetPlayers.remove(player);
                  this.cancel();
                }
 else                 if (player.getLocation().getWorld().getName().equalsIgnoreCase(Settings.worldName)) {
                  Collection<PotionEffect> activePotions=player.getActivePotionEffects();
                  for (                  PotionEffect s : activePotions) {
                    if (s.getType().equals(PotionEffectType.WATER_BREATHING)) {
                      wetPlayers.remove(player);
                      this.cancel();
                      return;
                    }
                  }
                  for (int y=player.getLocation().getBlockY() + 2; y < player.getLocation().getWorld().getMaxHeight(); y++) {
                    if (!player.getLocation().getWorld().getBlockAt(player.getLocation().getBlockX(),y,player.getLocation().getBlockZ()).getType().equals(Material.AIR)) {
                      wetPlayers.remove(player);
                      this.cancel();
                      return;
                    }
                  }
                  if (Settings.rainDamage > 0D) {
                    double health=player.getHealth() - (Settings.rainDamage - Settings.rainDamage * getDamageReduced(player));
                    if (health < 0D) {
                      health=0D;
                    }
 else                     if (health > 20D) {
                      health=20D;
                    }
                    player.setHealth(health);
                    player.getWorld().playSound(playerLoc,Sound.FIZZ,3F,3F);
                  }
                }
 else {
                  wetPlayers.remove(player);
                  this.cancel();
                }
              }
            }
.runTaskTimer(plugin,0L,20L);
          }
        }
      }
    }
  }
  if (!block.isLiquid()) {
    return;
  }
  if (playerLoc.getBlockY() < 1) {
    final Vector v=new Vector(player.getVelocity().getX(),1D,player.getVelocity().getZ());
    player.setVelocity(v);
  }
  if (burningPlayers.contains(player)) {
    return;
  }
  if (Settings.allowSpawnNoAcidWater) {
    if (playerLoc.getBlockY() > Settings.sea_level) {
      if (plugin.getGrid().isAtSpawn(playerLoc)) {
        return;
      }
    }
  }
  if (block.getType().equals(Material.STATIONARY_WATER) || block.getType().equals(Material.WATER)) {
    Entity playersVehicle=player.getVehicle();
    if (playersVehicle != null) {
      if (playersVehicle.getType().equals(EntityType.BOAT)) {
        return;
      }
    }
    Collection<PotionEffect> activePotions=player.getActivePotionEffects();
    for (    PotionEffect s : activePotions) {
      if (s.getType().equals(PotionEffectType.WATER_BREATHING)) {
        return;
      }
    }
    burningPlayers.add(player);
    new BukkitRunnable(){
      @Override public void run(){
        if (player.isDead()) {
          burningPlayers.remove(player);
          this.cancel();
        }
 else         if (player.getLocation().getBlock().isLiquid() && player.getLocation().getWorld().getName().equalsIgnoreCase(Settings.worldName)) {
          if (!Settings.acidDamageType.isEmpty()) {
            for (            PotionEffectType t : Settings.acidDamageType) {
              if (t.equals(PotionEffectType.BLINDNESS) || t.equals(PotionEffectType.CONFUSION) || t.equals(PotionEffectType.HUNGER)|| t.equals(PotionEffectType.SLOW)|| t.equals(PotionEffectType.SLOW_DIGGING)|| t.equals(PotionEffectType.WEAKNESS)) {
                player.addPotionEffect(new PotionEffect(t,600,1));
              }
 else {
                player.addPotionEffect(new PotionEffect(t,200,1));
              }
            }
          }
          if (Settings.acidDamage > 0D) {
            double health=player.getHealth() - (Settings.acidDamage - Settings.acidDamage * getDamageReduced(player));
            if (health < 0D) {
              health=0D;
            }
 else             if (health > 20D) {
              health=20D;
            }
            player.setHealth(health);
            player.getWorld().playSound(playerLoc,Sound.FIZZ,2F,2F);
          }
        }
 else {
          burningPlayers.remove(player);
          this.cancel();
        }
      }
    }
.runTaskTimer(plugin,0L,20L);
  }
}

Fixed version (ground truth):
@EventHandler(priority=EventPriority.LOWEST,ignoreCancelled=true) public void onPlayerMove(PlayerMoveEvent e){
  final Player player=e.getPlayer();
  if (player.isDead()) {
    return;
  }
  if (!player.getWorld().getName().equalsIgnoreCase(Settings.worldName)) {
    return;
  }
  if (player.isOp()) {
    if (!Settings.damageOps) {
      return;
    }
  }
 else   if (VaultHelper.checkPerm(player,Settings.PERMPREFIX + "String_Node_Str") || VaultHelper.checkPerm(player,Settings.PERMPREFIX + "String_Node_Str")) {
    return;
  }
  if (player.getGameMode().equals(GameMode.CREATIVE)) {
    return;
  }
  final Location playerLoc=player.getLocation();
  final Block block=playerLoc.getBlock();
  final Block head=block.getRelative(BlockFace.UP);
  if (Settings.rainDamage > 0D && isRaining) {
    Biome biome=playerLoc.getBlock().getBiome();
    if (biome != Biome.DESERT && biome != Biome.DESERT_HILLS && biome != Biome.DESERT_MOUNTAINS && biome != Biome.SAVANNA && biome != Biome.SAVANNA_MOUNTAINS && biome != Biome.SAVANNA_PLATEAU && biome != Biome.SAVANNA_PLATEAU_MOUNTAINS && biome != Biome.MESA && biome != Biome.MESA_BRYCE && biome != Biome.MESA_PLATEAU && biome != Biome.MESA_PLATEAU_FOREST && biome != Biome.MESA_PLATEAU_FOREST_MOUNTAINS && biome != Biome.MESA_PLATEAU_MOUNTAINS && biome != Biome.HELL) {
      boolean hitByRain=true;
      for (int y=playerLoc.getBlockY() + 2; y < playerLoc.getWorld().getMaxHeight(); y++) {
        if (!playerLoc.getWorld().getBlockAt(playerLoc.getBlockX(),y,playerLoc.getBlockZ()).getType().equals(Material.AIR)) {
          hitByRain=false;
          break;
        }
      }
      if (!hitByRain) {
        wetPlayers.remove(player);
      }
 else {
        boolean acidPotion=false;
        Collection<PotionEffect> activePotions=player.getActivePotionEffects();
        for (        PotionEffect s : activePotions) {
          if (s.getType().equals(PotionEffectType.WATER_BREATHING)) {
            acidPotion=true;
          }
        }
        if (acidPotion) {
          wetPlayers.remove(player);
        }
 else {
          if (!wetPlayers.contains(player)) {
            wetPlayers.add(player);
            new BukkitRunnable(){
              @Override public void run(){
                if (!isRaining || player.isDead()) {
                  wetPlayers.remove(player);
                  this.cancel();
                }
 else                 if (player.getLocation().getWorld().getName().equalsIgnoreCase(Settings.worldName)) {
                  Collection<PotionEffect> activePotions=player.getActivePotionEffects();
                  for (                  PotionEffect s : activePotions) {
                    if (s.getType().equals(PotionEffectType.WATER_BREATHING)) {
                      wetPlayers.remove(player);
                      this.cancel();
                      return;
                    }
                  }
                  for (int y=player.getLocation().getBlockY() + 2; y < player.getLocation().getWorld().getMaxHeight(); y++) {
                    if (!player.getLocation().getWorld().getBlockAt(player.getLocation().getBlockX(),y,player.getLocation().getBlockZ()).getType().equals(Material.AIR)) {
                      wetPlayers.remove(player);
                      this.cancel();
                      return;
                    }
                  }
                  if (Settings.rainDamage > 0D) {
                    double health=player.getHealth() - (Settings.rainDamage - Settings.rainDamage * getDamageReduced(player));
                    if (health < 0D) {
                      health=0D;
                    }
 else                     if (health > 20D) {
                      health=20D;
                    }
                    player.setHealth(health);
                    player.getWorld().playSound(playerLoc,Sound.FIZZ,3F,3F);
                  }
                }
 else {
                  wetPlayers.remove(player);
                  this.cancel();
                }
              }
            }
.runTaskTimer(plugin,0L,20L);
          }
        }
      }
    }
  }
  if (!block.isLiquid() && !head.isLiquid()) {
    return;
  }
  if (playerLoc.getBlockY() < 1) {
    final Vector v=new Vector(player.getVelocity().getX(),1D,player.getVelocity().getZ());
    player.setVelocity(v);
  }
  if (burningPlayers.contains(player)) {
    return;
  }
  if (Settings.allowSpawnNoAcidWater) {
    if (playerLoc.getBlockY() > Settings.sea_level) {
      if (plugin.getGrid().isAtSpawn(playerLoc)) {
        return;
      }
    }
  }
  if (block.getType().equals(Material.STATIONARY_WATER) || block.getType().equals(Material.WATER) || head.getType().equals(Material.STATIONARY_WATER)|| head.getType().equals(Material.WATER)) {
    Entity playersVehicle=player.getVehicle();
    if (playersVehicle != null) {
      if (playersVehicle.getType().equals(EntityType.BOAT)) {
        return;
      }
    }
    Collection<PotionEffect> activePotions=player.getActivePotionEffects();
    for (    PotionEffect s : activePotions) {
      if (s.getType().equals(PotionEffectType.WATER_BREATHING)) {
        return;
      }
    }
    burningPlayers.add(player);
    new BukkitRunnable(){
      @Override public void run(){
        if (player.isDead()) {
          burningPlayers.remove(player);
          this.cancel();
        }
 else         if ((player.getLocation().getBlock().isLiquid() || player.getLocation().getBlock().getRelative(BlockFace.UP).isLiquid()) && player.getLocation().getWorld().getName().equalsIgnoreCase(Settings.worldName)) {
          if (!Settings.acidDamageType.isEmpty()) {
            for (            PotionEffectType t : Settings.acidDamageType) {
              if (t.equals(PotionEffectType.BLINDNESS) || t.equals(PotionEffectType.CONFUSION) || t.equals(PotionEffectType.HUNGER)|| t.equals(PotionEffectType.SLOW)|| t.equals(PotionEffectType.SLOW_DIGGING)|| t.equals(PotionEffectType.WEAKNESS)) {
                player.addPotionEffect(new PotionEffect(t,600,1));
              }
 else {
                player.addPotionEffect(new PotionEffect(t,200,1));
              }
            }
          }
          if (Settings.acidDamage > 0D) {
            double health=player.getHealth() - (Settings.acidDamage - Settings.acidDamage * getDamageReduced(player));
            if (health < 0D) {
              health=0D;
            }
 else             if (health > 20D) {
              health=20D;
            }
            player.setHealth(health);
            player.getWorld().playSound(playerLoc,Sound.FIZZ,2F,2F);
          }
        }
 else {
          burningPlayers.remove(player);
          this.cancel();
        }
      }
    }
.runTaskTimer(plugin,0L,20L);
  }
}