-2019 mac pro (3.2 GHz 16-core Xeon W, 128GB DDR4, Radeon Pro W5700X 16GB)
Both the imac and mac pro absolutely crush anything I throw at it (4k Raw, Red raw, feature length timelines, etc.) But, when I throw a freaking cell phone video at it, the entire system crashes. Everything I've found online says either A) people's systems aren't powerful enough, or B) to just revert to an older version of premiere. I've addressed both of those things and am still having the problem.
Crash, Error or problem, Formats, Freeze or hang, Performance
While I can't say I've seen a full computer shut down happen from any type of video, whether on Mac or PC, I will say that cell phone video is probably the worst video you can edit with, especially the HEVC/VFR combo. If you transcode the media to correct the VFR does that help? I realize that doesn't necessarily address the crashing, but a lot of cell phone video ends up needing to be transcoded anyway.
Have you updated all the GPU drivers on those machines?