Marking email as unread issue in Outlook app If I want to mark an email as unread in my Outlook app, I have to do it twice, because after the first time it changes back to the 'read' status (after a few seconds).

The problems occurs on a OnePlus 5T phone running Android 8.0.0 and I haven't found anyone else online reporting this small but annoying issue. It looks like a bug to me, but maybe someone else has encountered this as well or has some ideas to solve this?
Outlook's support team helped me.
They suggested to delete my account, subsequently clear the application's cache and then to add my account again.

Update: This seemed to work in the very beginning, but the issue actually persists.

Update2: The Outlook development team is investigating the matter. We'll have to wait for an update.

Update3: The issue is resolved since some time, presumably because Outlook fixed this bug and updated the app.