I thought it might be an extension[0], but its happening on chrome on my laptop too.
[0]: I had an idea to create an extension that hides every number >4 on the web, so that i am not bothered with "gamification".. but its not that
Maybe something on YouTube got updated, and you were seeing some cached bit of code that didn't jibe right.
Hope it is that easy for you, and it isn't a bigger problem.