DarthEmpress I would suggest they start with the processor, swapping in something more mid-tier (i5-13400 or so, which is still great for Sims 4) so you're not running into the common issue with higher-end CPUs. An issue with the processor could account for everything you're seeing. After that, they should test the RAM. And they should of course look at the motherboard, to check for swollen capacitors and the like.
But this really could be anything, unfortunately. If these people know what they're doing, they might be best served to just do some live debugging and see if they can catch the culprit that way.