Disconnected when riding a dragon
further rejoins result in a crash/disconnect
fixed itself after I disabled this mod (and iris)

https://gist.github.com/programaus/20117ee467b6d0583226540e2fd84380
neoforge (1.)21.1.180
not enough animations 1.9.3-1.21 - NeoForge

Report this to parCool, it's a crash on their end.