The layer controls for my mask don't line up with the mask edge

Hello. I've had this a couple of times and I'm not sure why it's doing it.

The pink line is the layer controls for my mask, the pen lines I drew to make the mask. After a few keyframes of moving the mask path, the mask drifts away from the edge as seen in the photo.

There are no other layers affecting this mask, so why is it drifting? and has anyone else noticed this before?

I'm using posterize time if that affects it at all.