I was playing in a recently-made world when I placed a Jar with a Butterfly mob from the mod Terraincognita. After some seconds, the game crashed. I don't know if it was the exact cause of the crash or if coincidentally something else happened and caused the crash, but either way here's the crash log:
crash-2021-05-27_15.06.59-client.txt

yup that's a bug. was introduced last version and happens if you click on a jar that has a mod inside with a mob. will fix next update

so basically, it happens when you right click on a jar with a mob from another mod?

happened when you right click on then with anything. fixed now