"Render thread/WARN]:The client is missing shield data from the server! This includes the default shield data! Please report this bug to Infernal Studios." message is clogging the log ( like more then 100 lines) and slowing world generation time
version 1.20.1 forge

The log spam is my mistake. I'll make it only display once the next time I get a chance to work on this.

Aside from that, that log message doesn't say much. Can you share what mod versions are being used in the client and server?