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. didnt do any dns stuff. but again that version 1709.
btw 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 still works.