I spent a bit of time checking into this and there are a few oddities with the Q2A microformats.
The microformat spec requires the "updated" and "entry title" fields, as well as "fn" (full name). Not sure if it was always like that or if it changed, but a similar question here from 2013 also has the same problem. There is also an answer there if you want a quick solution.
Q2A currently shows "published" on posts and "updated" only if a post was actually updated in some way. But I can change that to "published updated" when there are no updates yet.
Q2A uses "nickname" on usernames, but I can add "fn" there just to satify the requirement.
We don't have a title for comments or answers so it's difficult to know what to do there. Also it turns out the "entry-title" for the question is in the wrong place and has no effect... The linked answer above just puts entry-title on the username which is probably the only thing we can do right now.
The above changes will be put into the next release (1.7.0 or 1.7.1) as a quick fix.
However, I don't think the hentry microformat is really suitable for individual posts, only the question as a whole. There is a microforamts-2 spec but search engines don't support it. They seem to prefer schema.org microdata, and in fact there are special ones for Q&A sites that Stack Overflow and Yahoo Answers are both using.
So I think for the future, it would be a better idea to support schema.org microdata and scrap the current microformats.