I had a mini panic attack when I refreshed a waiting PR and was suddenly logged out. I take all the suggested precautions with my GitHub account, so while my mind did wander to the worst case, I figured it was just a weird cookie interaction on my machine.
If anyone at GitHub is reading this, it would have been nice to see an alert with this info on GitHub's status page, which is the first place I checked to see if it was a known issue.