Have you tried Memtest86? Run that and make sure the ram is working. And if you remember the ram dimm you used for the 1x8, try taking one stick out and putting one in the dimm, trying memtest86, then putting the next one in, etc...
Sometimes Ryzen can be wonky with memory, so maybe try underclocking it to 2400 mhz (adjust the voltage as well) and see if that helps.
Best of luck.