Sounds like a css issue - do you have anything in additional css?
I use Moodlecloud. When I came into work on Monday, they had updated and then I got this problem. I have never had this type of problem before, and I assure you I personally didn't change anything over the weekend. This update has made my gradebook incredibly difficult to read.
I am having the same issue. No modifications done to the moodle instance. Also replicated the issue in different courses and different browsers. Cleared cache/cookies with no luck

Thank God! I thought I had done something and was going into a panic! Now how do we get it back to normal? I have trainers tearing their hair out!
Who fixed something? Are you Moodle cloud users? If this is your install, the only thing that might have been fixed is a browser...