Came from https://www.mcbbs.net/thread-1179223-1-1.html which posted this log: https://paste.ubuntu.com/p/xZn3DJ2fBx/

Judging by the stack trace I assume it is 1.12.2. Problematic line:

According to the log message, it is suggested to add

buf.release();

at the end of the writeBytes(ByteBuf), to avoid potential memory leak.

Further reading:
https://netty.io/wiki/reference-counted-objects.html

Will be fixed in the upcoming CreativeCore release. Probably will be there in a week or so.

New version is out!