Outlook 365 doesn't always mark emails as read

Outlook version
Outlook 2016 64 bit
Email Account
IMAP
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
 
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