Drivers not working as expected

I have a character with a multi-part armature. One for the mesh, then one for IK and another for FK. I have drivers set up to switch from one mode to the other.

Lately I’ve noticed if I “turn off” IK and try to use only FK I get unreliable results. I have to pose both the IK and FK rigs to get the pose. This is a real pain.

Has the way the drivers work changed? I’m currently using 2.83.1 on Fedora 32. I started seeing the problem in 2.82 (I think).