Are you using Windows 10? Then most likely it was some forced Windows update which included new drivers for your AMD GPUs. I ran into this problem a few times in the past. It would either not hash at all because all the overclocking settings were reset OR it would hash at a slow speed because compute mode was disabled by default.
It was a pain in the butt to disable but somehow with some reg hack I was able to prevent any updates from happening again. Search the web and there is a guide on how to disable Windows 10 updates. Its pretty indepth and you need to block access to certain DNS hosts.
there are (or were) a couple services that i disabled in win10 1709 and that machine has not updated since. pretty sure i didnt do any dns stuff (for instance my hosts file is still stock). but again that version 1709.
that was from a guide i found online a couple years ago. so i have no idea where i got it or if that method (disabling various services only) still works.
I'm still on version 1709 too.
Here is that guide:
1) How to Disable Drivers Update in Windows 10:
Windows key+R > Type gpedit.msc and hit Enter > Navigate to: Computer Configuration > Administrative Templates > Windows Components > Windows Update.
Double-click "Do not include drivers with Windows Update" and set it to
Enabled.
2) How to Disable Windows 10 Update:
Computer Configuration > Administrative Templates > Windows Components > Windows Update.
Double-click "Configure Automatic Updates" and set it to
Disabled.
One of my rig updated to windows version 2004 and it seems that there is no changes in all my cards and also to mining speed, I have sapphire nitro+ rx 570 8gb and also the radeon software automatically updated to radeon 20.9.2