By: Nydia

Just had the exact same issue on my Excel, with nothing working to fix it, when my colleague suggested me to copy/paste the cell to an adjacent empty cell. Voila, it worked, and then I simply dragged the copied cell to replace the one not working. Curiously enough, all other non-visible comments became visible after that, although displaced to a corner and compressed, so I had to expand them when editing. But no need to do anything else. Hope this helps if anyone else is still struggling with this annoyance!