This does sound very strange. One theory would have to be that it’s some kind of bad state in your browser. You did mention that you tried clearing the cache and logging in again, so maybe it’s just a plain bug in your browser or in your browser plugins. I would suggest trying a completely different browser and different computer. E.g. if you’ve been using Chrome on a Windows laptop, try it using Safari on a Mac or Firefox on Windows or use a tablet instead of a computer.
The other theory is that the bad state is in your account on the Coursera website, so Tom’s suggestion of contacting the Coursera Help Center would be the next step if my other suggestion above doesn’t work.