Imported PSD layers flashing randomly when animated in Premiere

I will try to keep this brief, though this issue has been plaguing me for weeks and I have had now three remote sessions with Adobe Support, the latest of which seemed to stop the problem, and during the first of which the support tech recommended downloading the PP Beta. So this morning I installed the newest version of the beta (22.0.0 Build 144) — and the problem is back. I'm aware that Adobe doesn't support beta versions, but I have a client who's been waiting patiently for this two-minute animation and I don't know what else to do. See the attached video to see what I'm talking about (problem evident at :20 seconds, :22 and :25).

This began on PP 15.4.1 on a Mac M1 Mini 2020 with 16GB RAM running Big Sur 11.5.2, the first project I started on this new-to-me machine. This project has about 90 layers, imported as sequences from 12 separate PSD files. It seems that the more layers I add and animate (mostly using PP's built-in gradient wipe transition, and a few Film Impact transitions, but it happens just as often and randomly without any third-party transitions).

It seems to me to be an encoding problem; it happens if I render the timeline — and, tragically, on export via AME. (The previous beta was the first version in weeks in which it did NOT happen on export, which is why I resumed work on the project. And now it's back: The attached mp4 is an export.)

I have reset preferences. I have cleared caches. I have tried both software and hardware encoding, both in Premiere and for exports (although the latest beta introduced a new bug that won't let me click on certain dropdowns, including the one in the export panel that selects Hardware or Software Encoding!!).

If any of my support forum brothers and sisters who know a lot more about how Premiere works than I do (which is probably all of you) can offer any help or ideas, I would be most grateful. From conversations with Adobe's support personnel over the last couple of weeks, I'm starting to think that Adobe still doesn't quite know how Apple's M1 chip (and the lack of a dedicated GPU) works.

Just please don't make me switch to Final Cut, which I'm guessing does play nice with the M1.