I perform literally hundreds of effects in Premiere a week and I have never seen this before. I put an Earth image on timeline, made two keyframes - one is at normal position, second scaled up to make it look like it's zooming in - play the timeline and nothing happens. You can see the scale #'s moving but absolutely nothing happens in the monitor window. I tried exporting to see if you can see the scale and you can't see it there either.
I also closed the project and deleted all of the media cache files, then opened and tried again - nothing fixes it. Below are images - of first keyframe, second, and then the timeline playing and you'll see how scale #'s have changed but monitor image looks the same like it's stuck.
Error or problem
Freeze or hang