Thank you, StevenBenassi . Let me confirm but as far as I know, all our courses are on Rise. The Rise courses have embedded Story files but I doubt any errors on those files would affect the table of contents, but please correct me if I am wrong here.
I'm not sure if this is isolated to a single browser because our users usually use their own devices and they all have preferences. So far, I've only encountered this from a handful of users, most using Chrome and Edge (which is techically still Chrome underneath the hood), with no adblockers and the like installed,, and were previously resolved by clearing their cache.