I just received it and when I wanted to turn on ryzen master it didn't let me, MOBO is ok, a r3 1200 worked fine yesterday.
MOBO-Gigabyte Aorus B450
RAM-Corsair 16GB 3200
Have you updated the bios for the Ryzen3000 series?
Yes, would it even start if I wouldn't but I got it fixed, reinstalling windows, most probably a driver issue
I had the same problem as you when i get my r5 3600, it was like 2c/4t in tash manager and hwinfo, to fix it i went to msconfig (press windows button + R or right click on windows icon and execute), go to ''boot'', ''advanced options'', uncheck ''number of processors'', click ok, apply and reboot the computer. After if it works you can check ''number of processors'' and select the maximum amount.
(Edit : I didn't see that you solved the problem lol ;( )