I have determined that Requiem 1.7.6 crashes whenever I shift click fuel out of a furnace. I have disabled all mods except for Requiem and Fabric API (0.34.2+1.16) and tried both with and without Cloth Config (4.11.26). This does not occur with Requiem disabled, so I'm fairly certain that it is the cause. It happens both in singleplayer and multiplayer.

It seems to be a simple IndexOutOfBounds exception, though I won't act like those haven't kept me up into the late hours of the night before. I wish you the best of luck on this. If you need any more details that you think I can provide, please do let me know.

crash-2021-05-18_01.00.42-client.txt

After further testing, I found that Requiem 1.7.5 does not seem to have this issue, which would lead me to believe that this issue was introduced in 1.7.6 (maybe in this commit since it relates to shift clicking). I hope this extra information helps to narrow down the issue.

Found the issue, thanks for the detailed report !

<3 for jamalmarri, this is the best kind of report

I was about to report the same thing then I saw this. +1!