Version 6.0.37
I have tested 2 different types of image slideshows: with the Collection component and using GoogleDrive component. In each case, I want to cycle through a series of images with a cross-disolve transition between each one. They both work fine, but if I put an image mask above either of these, the images pop in front of the mask during the transition and then pop behind the mask (where they should be) after the transition is complete.
I have done this several different ways with the same result. The last was to create a new channel that was at the top-most layer and putting the image mask in a scene. I have also just put the image itself in the channel (with no scene).