A very common situation: there is change in flight, with several versions in the works. Different comment threads are associated with code in different patchsets. When the reviewer/submitter presses the "publish comments" button, only the draft of the current patchset is published. This often causes unpublished drafts.
It would be more robust if all existing draft comments (on all patchsts) were included in the email.
Ideally, all comment threads should be promoted to the latest patchset (which of course is not always possible) - this would make the review easier with all comment threads visible on the latest patchset.
This issue is extremely annoying. It is not at all obvious how to publish
draft comments on earlier patch set (you have to select a file from that
patch and then hit 'r' from there to publish your review for that patch