I do get an error in event log about the display driver crashing so it's sorta a place to start I guess but why it's doing that I don't know. It lasted the rest of the night, so I suspect I have 2 issues going on, the heat issue which is most likely solved otherwise I think it would have died right away, and now some random software issue.
The mini DP to regular DP adapters may also be at fault, when I initially setup my PC at the office I had to play around with them to get all displays to work. So maybe something slightly moved and triggered this. They are kind of dodgy.
My next shift is going to be at home so I'm bringing my PC and I have a whole week off so think I will leave it turned on at home to see if it does it again. If yes I will come pull the GPU from my old PC at the office and swap it to see if it solves the issue. The fact that it's so random is going to make this a pain to troubleshoot though. It lasted 3 days before doing this.