Not sure what causes the crash, but sometimes, seemingly completely randomly while playing on a world, you'll get disconnected with the error "Network Protocol Error" even though you're playing single player. Attempting to reconnect to the world forces it to disconnect you again with the same error, essentially making that world inaccessible until you remove either this mod or Modern Fix.

Hi, thanks for the report. I'll try to investigate the cause of the issue as soon as I can