I'm not sure why this is happening but my game decided it was going to crash when I went to sleep and woke up in the abyss thanks to the abyss II mod. However, upon waking up in the Abyss my game froze and crashed with java.util.ConcurrentModificationException: null error it's incredibly annoying because I was in the process of recording a video for YouTube when this happened. It seems like it has something to do with this mods improved sleeping module but I'm not sure.

Crashlog

I have the same problem
I asked the author of The Abyss:
https://www.curseforge.com/minecraft/mc-mods/the-abyss-chapter-ii#c343

I've seen this issue before. I'm not sure why this happens, it seems to be some weird sort of multithreading problem.

I have also the same Problem
But the wierd is, its dont Crash every Time, its like 1/10 % Chance to Crash
We using Better Minecraft Modpack
Only the Server Crashing, not the Clients
Crashlog

Hello! Quark's moved to 1.18 now-- unfortunately, this means that (unless your bug is critical and/or game-breaking), we're closing support for issues filed for versions prior to it (e.g. Quark on 1.16).

If your issue still occurs on 1.18, or if your issue happens to be rather critical (e.g. consistently crashing the game with no other mods present), please leave another note or open a new issue. Thanks for your cooperation!