Program: 11817
Project: 11817
Buggy source:
public static CompoundTag generatePlayer(UUID id){
  World defaultWorld=TridentServer.WORLD;
  Coordinates spawnLocation=defaultWorld.spawnLocation();
  CompoundTagBuilder<NBTBuilder> builder=NBTBuilder.newBase(id.toString());
  builder.stringTag("String_Node_Str",String.valueOf(counter.incrementAndGet()));
  builder.longTag("String_Node_Str",id.getMostSignificantBits());
  builder.longTag("String_Node_Str",id.getLeastSignificantBits());
  ListTagBuilder<CompoundTagBuilder<NBTBuilder>> pos=builder.beginListTag("String_Node_Str",TagType.INT);
  pos.tag((int)spawnLocation.x());
  pos.tag((int)spawnLocation.y());
  pos.tag((int)spawnLocation.z());
  builder=pos.endListTag();
  ListTagBuilder<CompoundTagBuilder<NBTBuilder>> motion=builder.beginListTag("String_Node_Str",TagType.INT);
  motion.tag(0);
  motion.tag(0);
  motion.tag(0);
  builder=motion.endListTag();
  ListTagBuilder<CompoundTagBuilder<NBTBuilder>> rotation=builder.beginListTag("String_Node_Str",TagType.INT);
  rotation.tag(0);
  rotation.tag(0);
  builder=rotation.endListTag();
  builder.floatTag("String_Node_Str",0);
  builder.shortTag("String_Node_Str",(short)0);
  builder.shortTag("String_Node_Str",(short)0);
  builder.byteTag("String_Node_Str",(byte)1);
  builder.byteTag("String_Node_Str",(byte)0);
  builder.intTag("String_Node_Str",Dimension.OVERWORLD.asByte());
  builder.intTag("String_Node_Str",900);
  builder.stringTag("String_Node_Str","String_Node_Str");
  builder.byteTag("String_Node_Str",(byte)0);
  builder.byteTag("String_Node_Str",(byte)0);
  builder.compoundTag(new CompoundTag("String_Node_Str"));
  builder.intTag("String_Node_Str",Dimension.OVERWORLD.asByte());
  builder.intTag("String_Node_Str",GameMode.SURVIVAL.asByte());
  builder.intTag("String_Node_Str",0);
  builder.intTag("String_Node_Str",0);
  builder.intTag("String_Node_Str",20);
  builder.floatTag("String_Node_Str",0F);
  builder.floatTag("String_Node_Str",0F);
  builder.intTag("String_Node_Str",0);
  builder.intTag("String_Node_Str",0);
  builder.intTag("String_Node_Str",0);
  builder.intTag("String_Node_Str",0);
  builder.intTag("String_Node_Str",0);
  builder.listTag(new ListTag("String_Node_Str",TagType.COMPOUND));
  builder.listTag(new ListTag("String_Node_Str",TagType.COMPOUND));
  builder.intTag("String_Node_Str",0);
  builder.compoundTag(NBTSerializer.serialize(new PlayerAbilities(),"String_Node_Str"));
  return builder.endCompoundTag().build();
}

Fixed version (ground truth):
public static CompoundTag generatePlayer(UUID id){
  World defaultWorld=TridentServer.WORLD;
  Coordinates spawnLocation=defaultWorld.spawnLocation();
  CompoundTagBuilder<NBTBuilder> builder=NBTBuilder.newBase(id.toString());
  builder.stringTag("String_Node_Str",String.valueOf(counter.incrementAndGet()));
  builder.longTag("String_Node_Str",id.getMostSignificantBits());
  builder.longTag("String_Node_Str",id.getLeastSignificantBits());
  ListTagBuilder<CompoundTagBuilder<NBTBuilder>> pos=builder.beginListTag("String_Node_Str",TagType.DOUBLE);
  pos.tag(spawnLocation.x());
  pos.tag(spawnLocation.y());
  pos.tag(spawnLocation.z());
  builder=pos.endListTag();
  ListTagBuilder<CompoundTagBuilder<NBTBuilder>> motion=builder.beginListTag("String_Node_Str",TagType.DOUBLE);
  motion.tag(0d);
  motion.tag(0d);
  motion.tag(0d);
  builder=motion.endListTag();
  ListTagBuilder<CompoundTagBuilder<NBTBuilder>> rotation=builder.beginListTag("String_Node_Str",TagType.FLOAT);
  rotation.tag(0f);
  rotation.tag(0f);
  builder=rotation.endListTag();
  builder.floatTag("String_Node_Str",0);
  builder.shortTag("String_Node_Str",(short)-20);
  builder.shortTag("String_Node_Str",(short)0);
  builder.byteTag("String_Node_Str",(byte)1);
  builder.byteTag("String_Node_Str",(byte)0);
  builder.intTag("String_Node_Str",Dimension.OVERWORLD.asByte());
  builder.intTag("String_Node_Str",900);
  builder.stringTag("String_Node_Str","String_Node_Str");
  builder.byteTag("String_Node_Str",(byte)0);
  builder.compoundTag(new CompoundTag("String_Node_Str"));
  builder.intTag("String_Node_Str",Dimension.OVERWORLD.asByte());
  builder.intTag("String_Node_Str",GameMode.SURVIVAL.asByte());
  builder.intTag("String_Node_Str",0);
  builder.intTag("String_Node_Str",0);
  builder.intTag("String_Node_Str",20);
  builder.floatTag("String_Node_Str",0F);
  builder.floatTag("String_Node_Str",0F);
  builder.intTag("String_Node_Str",0);
  builder.intTag("String_Node_Str",0);
  builder.floatTag("String_Node_Str",0);
  builder.intTag("String_Node_Str",0);
  builder.intTag("String_Node_Str",0);
  builder.listTag(new ListTag("String_Node_Str",TagType.COMPOUND));
  builder.listTag(new ListTag("String_Node_Str",TagType.COMPOUND));
  builder.intTag("String_Node_Str",0);
  builder.compoundTag(NBTSerializer.serialize(new PlayerAbilities(),"String_Node_Str"));
  return builder.endCompoundTag().build();
}