Brought to my attention by SuntannedDuck2
From: https://www.curseforge.com/minecraft/mc-mods/invmove?comment=8

Describe the bug
If a boolean value in the config (eg. enableMod = true) is set to a non-boolean value (eg. enableMod = "true") while in-game, the game crashes.

To Reproduce
Don't think you can reproduce with only InvMove, but a bug in the mod Commands4Configs lets this happen:
Generate a new singleplayer world.
Run "/config invmove CLIENT set General.enableMod true"
Open inventory
-> instant crash

Crash Log
(Normally you would put the crash log here but it's different for different config values and I already know the problem)

Version and Mod List
List the version of InvMove and the version of Forge the issue happens on:
InvMove: 0.4.1
Forge: 31.2.31

List any other mods being used (other than Cloth Config):
Commands4Configs - 1.0.0

While the root problem lies with the bug in Commands4Configs, I can fix it for my configs specifically by type-checking the config values.