masks don't live update while effects are applied
When you're animating a mask on a layer that has effects applied, the mask doesn't update live. You have to purge the memory or disable all the effects on the mask in order to be able to see the updated layer.
We need to see the mask updated even with effects applied.
Nate Foster commented
I've had this bug for a couple versions. it's Mocha. Somehow, Mocha is keeping AE from dumping the cache and redrawing the frame when a change is made. I've had this bug surface in renders as well. My work-around is to do all of my Mocha work on a Guide layer and then copy paste the needed masks/tracking data to other layers in my comp. I never use the plug in to create a matte.
Matt Lathrom commented
Bump this. Specifically, I've noticed this when the Mocha Effect is applied to a layer.