Reflection artifacts on edges of screen

Anyone know what could be the cause of these weird blocky reflection artifacts around the edge of the screen? They appear only on the reflective surface and always stay around the edge of the screen regardless of distance from the object.

I’m creating a video sequence, my work around is to make the frame wider and crop in post as they only appear at the edge of the frame.

I think this was an issue with the GPU, seems to be ok now on other renders since the machine has been rebooted.