Sure seems video-card related on the surface, but let's keep digging and cracking. Mobo is a possibility, but IMO a greater probability of failure (however intermittent) lies in RAM, and PSU. 18 months ago (june 2017) I built a home ESXi box around a Ryzen 5 1600, Asus Prime X370-PRO, and 64GB (4x 16GB) G.Skill Fortis (AMD-compatible
looks just like Aegis from G.Skill today) DDR4-2400. The doubled RAM over my Sandy/Ivy Bridge Xeons was letting me combine two hosts into one. It's a 64GB RAM kit, and all four sticks truly have sequential serial numbers. The only Newegg review for that kit is by me, and I praised it for passing Memtest with zero errors.
That's no longer the case. Depending on speeds and DIMM combinations, it's almost impossible to get any pair of the 4 DIMMs to pass MemTest, even at stock 2133. I even tried one run at 1866 and still errors. Thousands of errors. It may be rare, but RAM can go bad. Since this all unfurled about a month ago (by that I mean instability became intolerable over the past 18 months, leading to testing and parts-swapping), I swapped over Mushkin DDR4-2400 (32GB, 16x2) into the host and it passes MemTest and has been stable. I moved the G.Skill (32GB, 16x2 at a time) into my main Windows PC (also Ryzen 5 1600, with the similar Asus ROG Strix X370-F). Only one combination of the 4 DIMMs from the 64GB kit, consisting of 32GB (16x2) will pass MemTest in this alternate motherboard.
Since I just cut the host's RAM in half, I added a NUC7i7BNH (Baby Lake) with 32GB of G.Skill SO-DIMMs (16x2) to my vSphere. This was also MemTested in 2017 when assembled, and again in 2018 when it (probably a different unit) came back from RMA. Now it won't pass MemTest either, although there haven't been any ESXi PSODs like the Ryzen host had monthly-to-daily with G.Skill RAM.
TL;DR - always re-test memory even if it already checked out, when dealing with instability. Especially if that RAM is G.Skill. That's 6 DDR4-2400 DIMMs (two of them SO-DIMMs) that were fine 1 year and a half ago, and no longer are.
Be careful on inserting this (or any G34 chip) into the socket. Once you pull that restraining lever, it is either a good install or a piece of silicon jewelry.