For anyone interested in the exciting conclusions... it worked fine in the 16x slot for 2 weeks and is still in there now
I put an I340-T4 in the 1x slot at the same time and left that running and that has been perfectly fine as well
It seems to be an incompatibility between the 1x slot and the I350 specifically but i'm not sure why. In either case, the issue seems to be resolved
It may be something specific to AM5 and the I350 in the 1x, or just the I350 and the 1x alone but if anyone else for some reason tries the same, at least you know what symptoms manifest and what the cause was
Thanks again for those that helped and commented