Mask is messing up background

I have a mask set up as a transition between backgrounds. The mask works fine but I have to leave the mask on for the entire duration that I want to show the background. This wouldn’t be a problem except that my scene moves from front to back and during that process the mask stops working and blocks my background. I have tried to move the mask backwards with the scene but I wasn’t able to get that to work. What should I do?

It is hard to give an answer on this without seeing the project.
Can you post a screen capture or send one to