I just experienced a very similar issue. In this case I have an image sequence with an object buffer pass precomped with collapsed transformations. For some reason it just uses one frame of the object buffer pass to mask the layer, yet when I go inside the comp it acts normal. So outside of the precomp the matte doesn’t move, but inside it does.
Is it possible this is related to time remapping the precomp? I’ve since turned off time remapping with no effect, but it worked previous to me enabling it.