I have two clients launched, one of the instance was copied from the other by MultiMC. I joined a world using one client then put it to LAN, and the other client is unable to join the world, throwing an error description as was said in the title. These two clients, the original one and the copied one, have exactly the same list of mods, but, the original one was once used to test mods, that is to say, I have some mods installed and deleted quite a couple of times. It has already confused me few days ago when I try to execute /fill command I can still see those block IDs even if the mod they belong to was deleted from the instance. And the log seems to prove that the error is caused by those remaining registries:

[16:55:52] [Netty Client IO #0/ERROR] [ne.mi.fm.ne.NetworkRegistry/NETREGISTRY]: Channels [patchouli:main,curios:main,modernui:main_network] rejected vanilla connections
[16:55:54] [Render thread/ERROR] [ne.mi.re.GameData/REGISTRIES]: Unidentified mapping from registry minecraft:block
anointeditems:anointing_table: 1351
antimatter:invalid_ev: 1433
antimatter:invalid_hv: 1432

......

following seas of things that actually got deleted already.

 

So I guess if there's a way to wipe these out, the problem could be solved.

1 hour ago, diesieben07 said:

This is a known issue with "Open to LAN". You have to use a real server for the time being.

Ok, then how about the remaining registries