May have figured it out. There is the end of one of the copper strips on the end of the motherboard missing. The bit that goes into the motherboard slot, it seems that just the tip of the copper was scratched off of one of the many tabs, it's probably still touching the mobo connector but maybe...
Sorry for late reply, I checked Reliability History and have been getting Windows Hardware Errors for a while now it seems. Report is as follows:
Source
Windows
Summary
Hardware error
Date
19/03/2021 3:57 AM
Status
Report sent
Description
A problem with your hardware caused Windows to...
Not sure if it's a graphics card issue or not, I was leaning towards it at the start but not too sure now.
Basically, every so often my 3 monitors screens turn black for about 3 seconds, sound cuts out, sometimes my tabs switch, and weirdly my default sound device changes to something random...