Hey there!
I think I found an issue in XWiki 17.10.3 (XWiki Standard). The comment action buttons are often not clickable (they are not even focussed), depending on the scroll position.
I tracked it down to the #tourResumeContainer div or more specifically the .popover-content children div, which blocks access to the comment action buttons:
Note that the root cause you dug up is the most interesting part IMO.
The comment action buttons should move to the left on 18.X (which would solve your specific issue as a side effect), see Loading... . I’ve been spending time implementing those improvements and they are almost ready