I recently upgraded my confluence version from 5.7 to 8.6.2. Since then I have been unable to edit any documents.
I tried to do some progressive updates, move to 6.0 and 7.0 first, and those were fine. It seems that once collaborative editing came in the editing broke for my system. I can still create and delete pages, but there is no way to edit.
I've tried disabling collaborative editing, to see if that would resolve it, but the issue remains. Also confirmed that the port wasn't being used by any other service. At this point, I'm out of ideas for why this is happening and am hoping somebody else might have some suggestions.