Premiere Pro program window has been buggy since last update. Whenever you use a motion graphics file, he preview stretches horizontally whenever you click on the motion graphics file or scrub through the timeline. : https://streamable.com/1ua5cv
This is a new bug that wasn't there prior to last update. This is happening for both essential graphics that were made inside Premiere Pro, and ones that were made in After Effects. very annoying.
although it shouldn't cause the problem, but might give us a clue, are you working with material with non square pixel aspect ration (PAR)? Gotta say, life is much much simpler since square pixels became the norm...
Hi! Just letting you know that I have the exact same issue, it really slows down my workflow! Glad to hear that I am not the only one having this issue, I am also running the 15.2 version. I just installed my OS (Windows 10 Pro) again as Premiere was very slow but it didn't fix this one.