Email inbox notifying of emails but there's nothing in the inbox

[Gareth Watkins]

Myself and a few other users are experiencing an issue whereby the email thumbnail indicates new messages however, when we check the inbox, either nothing is present or less than the notified number.

Different users are also seeing different numbers of new messages. I get a count of 12 but an empty inbox and others get a count of 3. 

We've cleared caches, checked alternate browsers (Edge and chrome) and marked all other messages in other folders as read but the notification persists.

I've manually checked the linked mailbox in outlook to ensure the inbox is empty (it is) and have run out of things to try.

Users monitoring the mailbox for call updates are spending unnecessary time checking an empty inbox due to this issue. Is there anything else we can do to clear this back down to the correct amounts?