Is it solved?
I am also having issue of missing notifications in notification center for new mail on 10.3 beta 7 since beta 1.
The notifications either dont appear in notification center, or if they appear they disappear whenever the mail app is opened or on their own after 2 minutes.
Mail notifications vanish from the notification center immediately after the Mail App is opened and closed, even if no mail itself is opened.
I am on iOS 10.3 Beta 7.
Problem is not resolved even after Reset All Settings, hard reset, deleting the mail account and then adding again. I also did a fresh install of 10.3 beta 7 and restored from the iTunes backup- problem remains.