Outlook 365 doesn't always mark emails as read

Outlook version
Outlook 2016 64 bit
Email Account
I've set the reading pane up so that incoming emails are marked as read a second after selecting it. Now it does that at times, but mostly it gets unmarked a second being marked as read and I have to select another email and then the unmarked email to get marked as read.

is this a bug? It has been happening for quite awhile now.

Outlook Reading Settings.jpg