[Troubleshooting] Windows 10 + AMD graphics card, stuttering/low FPS for ~30 seconds after unlocking Windows and open windows rearranged across monitors

Hey, I have no idea if this is allowed here and I've been searching my fingers bloody over this, but the issue is so specific and non-descript, that I only find issues with games, etc.

My problem is as follows: I got a B450 Tomahawk (not max) latest BIOS and recently switched my GTX1070 for an RX 6700 XT (had to return due to coil whine) and now a RX 7800 XT.

Performance is great and everything is working fine. Drivers were wiped using DDU each time I swapped the cards and I upgraded my PSU to a be quiet 1000W 12M to accommodate the RX 7800 XT. I got a 3700x CPU and I am running three monitors, two via display port and one via HDMI.

Now my issue is really odd: Every time I put in an AMD graphics card, when I unlock Windows (after having it locked via Windows Key + L, NOT standby, NOT hibernate, here it works perfectly fine, only when unlocking), I now have insanely low fps/lag (as in my mouse moves super slowly and jumps around for a good 30 seconds, as well as windows from the main monitor being spread across the other two).

All monitors go on standby after a short period once the system is locked.

It's fine with the GTX 1070, so I must assume this is down to something with the graphics card or drivers or some weird power saving sleep state or something.

Anyone got any ideas that aren't: Wipe Windows, reinstall everything?

Thanks in advance!