For my setup, I use the M2 located near the cpu as the boot drive, without issue. This one is tied into the CPU, the lower one is tied into the chipset, both provide gen 4 x 4 speed.
Use the chipset drivers from AMD is wise and not an issue.
Make sure your running latest bios 1302
Make sure you have the ram placed in slots 2 & 4 from the cpu.
Where in the test does userbench bork ?
Near the end and after the gpu test is the sustained drive tests.
They are batch test run for approx from 60 or 30 seconds of each drive, (ie nvme, hdd etc.)
The order is normally boot drive first then each drive as was listed in the start tests, then when it completes and goes to url / final report screen.
Maybe worth checking if your Nvme drive has updated firmware as well.
Hope this is of help.