First place the mystery box, exit the world
Then load the world again
Loading progress will be stuck at 100%
This is a client test, the same will be true for the server

Hey there, i am unable to reproduce this problem. Please attach the Crashreport/Log file to this Ticket (Upload on Pastebin)
https://pixelmonmod.com/wiki/Finding_your_logs

Hi, I think I'm having the same issue (9.1.4 and 9.1.4a).
I had a player afk on a box when the crash happened.
https://paste.helpch.at/iyigiminod.pl - Crash

Debug log is too long to post in pastebin or helpchat. It currently gets stuck on loading a world and hangs there indefinitely. Please let me know if there's anything else I can provide.

I found out that the problem is MysteryBoxTileEntity.onLoad()
I tried writing a mixin that forbids onLoad from doing anything and solved the problem

I am unable to open your Link, it shows nothing.

Please reupload to pastebin.

Or just make /datapack list and /plugins . and send me a screenshot of those.

I am unable to reproduce this problem on 9.1.4

Can you try to use Forge Version 36.2.39
and journeymap 5.8.5 (journeymap doesnt need to be on the server, only client)

and without all the other mods.

Pixelmon, Forge, Byg, Map, and the 2 Compass mods. nothing else

I was unable to reproduce this Bug, but since a various of people reported this issue now, and i saw the issue in a screen-share myself, i will move this ticket to internal.

Thanks for reporting!