Crash occurred when an open backpack was closed. Here are the logs:
https://paste.dimdev.org/birexuxore.mccrash

Minecraft 1.12.2
Forge 14.23.5.2768
Leatherworks 1.75.5

Thanks!

Here is another crash which happened shortly after closing the backpack. Having players report these crashes a lot lately.
https://paste.dimdev.org/bawesocesi.mccrash

Minecraft 1.12.2
Forge 14.23.5.2796
Leatherworks 1.75.5

I believe you that it's happening but I can't replicate it, even after hours of trying to with all sorts of different things. I am left to believe it's an issue with one of the many core mods you have installed.
Best I can do is track it here for now. If you could send me what's actually in the bags in question when they are closed, that may be helpful