Ok so one stick is 100% bad. It causes memtest to just black screen. This happened when it was by itself in the second slot, and also with a good module in the second slot and having it in the 4th slot. I’m not sure when it exactly went black screen, but within 30 minutes of running the test for sure. System was unresponsive.
Nemix approved RMA of one stick so I’m going to proceed with that. In the meantime I’m only running 2 sticks in 2nd and 4th slot for proper dual channel.
When I was running 3 sticks dmesg only had one error, but I’m chalking that up to flex mode. I think Ryzen doesn’t like that. Once I get the replacement stick in I’ll be back up to all 4 DIMMs populated.