Since you changed CPU, clear cmos ones and also go to BIOS and save changes on exit - you don't need to change anything.
If this doesn't work, it could be memory. Ryzen are a bit more tricky as it comes to memory and also as always, some individual CPU's are better and others worse. Without knowing your memory speed or latency settings, I would probably start by either setting the memory to 3200Mhz if it is now higher, as that is the rated speed for that CPU, and/or just increse memory voltage to 1.375-1.4V and see if either helps.
CPU's with integrated graphics (especially AMD) to my knowledge are more sensitive to which memory they use. You could also - for testing - try one DIMM at a time (how many do you have? and what clockspeed?)
If this doesn't work, the thing is you changed CPU, so maybe you need to reinstall Windows. Some reviewers say that while computers usually work just fine without reinstalling, especially if you go from one brand (like Intel) to another (like AMD), you should reinstall as performance might not be as good as it should. I think Hardware Unboxed mentioned this when talking about benchmarking hardware.
EDIT: It coud also be a matter of some power saving setting. Just in case you have changed something in BIOS when you had previous CPU, maybe set it do default, then enable things like XMP, remember the memory speed and voltage settings, check you have virtualization enabled and... I'm not sure if APU's should have or support SAM?
