Hi
I'm in same club - changed from Nvidia to AMD and had similar issues - most likely you see very low GPU usage - perhaps 70 % and cpu the same. Could be many things - but a place to start is look at settings for your monitor. Do you have g-sync monitor ? Make sure in windows that monitor settings have correct refresh rate - if you have a 144 hz monitor - windows will set it at 60 hz - change it to 144 if such a monitor. Windows game mode - you can try to turn that off / on and see if that makes difference.
In AMD driver you can choose different modes - game mode, esport mode - etc... try the esport mode - turn off anti-lag, sharpening - turn it all off - v-sync always off. To the right you have freesync setting - if you do not have freesync monitor - it will set it to AMD optimized - turn that one off. All settings can be done globally or set for each game.
I think what you have here is a sync issue between card and monitor. I have 6900 xt and in BF5 I was suddenly below 100 fps on ultra - now I hit 200 (max) and have it cap'ed at 144 so it matches my monitor (gsync Acer predator).
Hope this is helpfull.