What I did was lower my DRAM voltage to 1.1v at 2133 MHz, and also increase the VDDP to 1.15. Both of these can be changed in 'OC tweaker' in the BIOS.

The DRAM voltage does seem low, but it has basically solved my problem as freezes are no longer a major issue. If 1.1v is unstable or you want a higher speed, you can probably try increasing the VDDP along with the DRAM voltage.

Since the problem was fixed by messing around with RAM voltages, the problem probably lies somewhere with the RAM and/or the PSU. 

once the computer has been running for a while and heated up, the stock voltage may suddenly not be enough.

increasing the voltage a bit can help keep it stable even with the increased temperature.

of course i'm just speculating, it could also be the memory controller, you could try raising SoC to 1.1v.

but i had a similar problem with a RAM overclock becoming unstable with increased ambient temps.

i wouldn't go over 1.35v vcore, 1.1v SoC, or 1.4v DRAM voltage.

it sounds like a ram issue IMO, i had similar issues while i was figuring out my overclock. ryzen sometimes has problems with ram even at stock settings.

if you're running stock, DRAM voltage should be 1.20v by default, try bumping it to 1.30v ~ 1.35v.

don't touch anything else, shouldn't need it if you're not overclocking.

it's possible you may need to adjust ram timings, i don't know if that kit has an XMP profile, but XMP settings usually are not well optimized for ryzen. i would expect it to be fine at stock though, so save that as a last resort.

it's also possible you just got bad ram. if you have any other ram laying around that you can swap it out for just to help narrow down the problem, that might be a good idea.

A new MSI B350M Gaming Pro has been ordered. Not a huge selection of M-ATX boards at my local dealer.

On to the online supplier to order a new motherboard.