Masks make footage disappear in program monitor

Premiere Beta v26.3.0.061

macOS Tahoe 26.4.1

In Color Mode, when I paste a mask from one clip to another, the footage disappears in the program monitor. If I delete that clip adjustment the video reappears in the program monitor. But if I try to create a new mask it turns black again. 

This creates two problems. First, I have to manually recreate vignettes and power windows for every single clip because I can’t copy and paste. Second, the clips that I have pasted a mask to (even if I delete it afterward or Undo) will no longer be able to receive a mask without going black in the program monitor. 

Is this a bug, or is this user error? 

I’ve tried offlining and relinking the clip, duplicating the footage in finder and relinking to the duplicate, clearing media cache, and duplicating the clip in the timeline.

Thanks for the help and insights!