I've read other issues that look similar but this doesn't seem to be what I'm experiencing.
I'm making a conveyor belt type thing. The conveyor belt is a long array of blocks (array modifier was applied) that has a curve modifier. I'm animating the x position of the blocks which turns the conveyor belt around.
The conveyor belt object is a rigid body that is passive / animated true / shape: mesh / source: deform (I tried final and it doesn't make a difference). Deforming is checked.
I have a bunch of rigid body boxes that are set to active. The boxes rest on top of the conveyor belt as if it wasn't modified with the curve.