Forge version 34.1.25
Crash Log here

Steps to reproduce:
Equip backpack from Quark Oddities. Use scroll wheel to place item into backpack.

Thanks for the log! I suspect this is an issue in Quark or in fastbench. Could you please report there too?

Hey there! One of the players on my server recently came across the same issue. I will report it to Quark and FastWorkbench too. Appears to be an issue between this mod and Quark.

This was on 1.16.4 and happened when middle clicking with the Quark Oddities backpack equipped.

Log file here

Thanks for reporting to their tracker! So was it fixed? Can I close this issue?