I won't duplicate the web pages about how to "clear cache" here since there are many articles about that. My thoughts are:
1. You used a web browser and the content was cached and may have to wait for it to take effect or "clear cache."
2. There is a real bug and you report that to the authors of the Facebook app or site.
I tried to change my cover photo using Facebook mobile app and wanted to revert one of my previously used cover photos that I used years ago. I went through the cover photos that appear above the profile picture (cover photos album on my Facebook profile). I clicked the photo to set as a cover , however it was updated as a new upload (duplicate) without retaining its likes and comments.
Then I logged into my Facebook account on my PC and deleted the duplicate and did the same process again. This time my previously used cover photo together with likes and comments was updated successfully without having any duplicate.
What could be the reason of this issue? I was wondering if this is something common, sort of a bug? My mobile operating system is iOS. I couldn't see either any complaints/examples on the internet with regard to such issue. Many thanks!