What it says on the tin! Can't join the server with this mod on both sides due to the following error:
https://mclo.gs/fGBRwrM

Some kind of issue with lens syncing? I don't have any custom lenses so I have no idea as to a possible cause here.

Fabric 1.20.1, mod version 1.7.16

Does that happen without other mods installed?

It does not! How strange. I'll try and troubleshoot this and get back to you

Bizarrely, the issue isn't happening on an identical local server (one I set up to make troubleshooting easier rather than dealing with a hoster). Looking further into it

Wiped the server and rebuilt from scratch, issue is gone. Consider me baffled. Sorry for the trouble and have a good one!

Weird thing is that you're not the first one to report that. Hopefully it won't happen again.