Seems to be an issue similar to the previous Tinkers Crash.
Right clicked a backpack on an armor stand, instant client crash
Client can no longer back in, but people outside of view range can log in.

#195

Running Enigmatica 6 version 0.5.7
Running sophisticatedbackpacks-1.16.5-3.0.3.297

Pastebin of crash log: https://pastebin.com/UsFjT5Z6 | https://pastebin.com/qsucwhhs

Edit: Workaround of /kill on the armor stand allowed me back in.

fixed in latest version

this is actually curious armor stands and an issue that I have fixed for curious itself in dev. So will be fixed with the next release.