Wow...I seem to have my first Mail "issue" since the betas this past Summer.
My badge is showing correctly that I have new mail. When I open the app, it usually defaults to "All Mail" inbox view since that is what I am usually on, but no new mail shows. If I "pull" down to refresh, still no new mail.
I have to back out to the "Mailboxes screen (where I see the number of new emails correctly in any of my 4 accounts. Then if I go back to "All Inboxes", they show up.
Certainly not the worst bug ever...I am getting notified and the mail is there...but a slight annoyance nonetheless. Trying a hard restart... 😉