Sometimes it is Windows.
I've had a 3000x, 1920x Threadripper, and now a 5950x.
Two out of the 3 new installs, Windows 10 defaulted to a Balanced Power setting. Control Panel => Power => advanced
If you open up advanced settings for the balanced theme, I found that 2 out of 3 times Windows defaulted to a processor minimum setting of 90% !!! I set this down to 15% and all was fine.