Program: 33818
Project: 33818
Buggy source:
/** 
 * Checks to see if a player is trespassing on another player's island Both players must be online.
 * @param owner - owner or team member of an island
 * @param target target of the query
 * @return true if they are on the island otherwise false.
 */
public boolean isOnIsland(final Player owner,final Player target){
  if (target.getWorld().equals(ASkyBlock.getIslandWorld()) || (Settings.newNether && Settings.createNether && target.getWorld().equals(ASkyBlock.getNetherWorld()))) {
    Location islandTestLocation=null;
    if (plugin.getPlayers().inTeam(owner.getUniqueId())) {
      if (plugin.getPlayers().getMembers(plugin.getPlayers().getTeamLeader(owner.getUniqueId())).contains(target.getUniqueId())) {
        return false;
      }
      islandTestLocation=plugin.getPlayers().getTeamIslandLocation(owner.getUniqueId());
    }
 else {
      islandTestLocation=plugin.getPlayers().getIslandLocation(owner.getUniqueId());
    }
    if (islandTestLocation == null) {
      return false;
    }
    int protectionRange=Settings.islandProtectionRange;
    if (getIslandAt(islandTestLocation) != null) {
      Island island=getProtectedIslandAt(islandTestLocation);
      if (island != null) {
        protectionRange=island.getProtectionSize();
      }
    }
    if (target.getLocation().getX() > islandTestLocation.getX() - protectionRange / 2 && target.getLocation().getX() < islandTestLocation.getX() + protectionRange / 2 && target.getLocation().getZ() > islandTestLocation.getZ() - protectionRange / 2 && target.getLocation().getZ() < islandTestLocation.getZ() + protectionRange / 2) {
      return true;
    }
  }
  return false;
}

Fixed version (ground truth):
/** 
 * Checks to see if a player is trespassing on another player's island Both players must be online.
 * @param owner - owner or team member of an island
 * @param target target of the query
 * @return true if they are on the island otherwise false.
 */
public boolean isOnIsland(final Player owner,final Player target){
  if (target.getWorld().equals(ASkyBlock.getIslandWorld()) || (Settings.newNether && Settings.createNether && target.getWorld().equals(ASkyBlock.getNetherWorld()))) {
    Location islandTestLocation=null;
    if (plugin.getPlayers().inTeam(owner.getUniqueId())) {
      if (plugin.getPlayers().getMembers(plugin.getPlayers().getTeamLeader(owner.getUniqueId())).contains(target.getUniqueId())) {
        return false;
      }
      islandTestLocation=plugin.getPlayers().getTeamIslandLocation(owner.getUniqueId());
    }
 else {
      islandTestLocation=plugin.getPlayers().getIslandLocation(owner.getUniqueId());
    }
    if (islandTestLocation == null) {
      return false;
    }
    int protectionRange=Settings.islandProtectionRange;
    if (getIslandAt(islandTestLocation) != null) {
      Island island=getProtectedIslandAt(islandTestLocation);
      if (island != null) {
        protectionRange=island.getProtectionSize();
      }
    }
    if (target.getLocation().getX() > islandTestLocation.getX() - protectionRange / 2D && target.getLocation().getX() < islandTestLocation.getX() + protectionRange / 2D && target.getLocation().getZ() > islandTestLocation.getZ() - protectionRange / 2D && target.getLocation().getZ() < islandTestLocation.getZ() + protectionRange / 2D) {
      return true;
    }
  }
  return false;
}