iPhone X Exchange Email Sync Issues

I have a problem with mail messages not being delivered to my inbox. They show up in Outlook app on iOS and also show up in Outlook on OS X but in the Apple Mail app, I might miss a few emails each day. This is a daily occurrence. It could be senders internally or externally. There doesn't seem to be a pattern. I have tried:

- deleting the Exchange account and re-adding it

- turning off Mail sync in settings and turning it back on

- factory resetting the iPhone and restoring as a new phone

None of the above is resolving the issue so it's leading me to believe it's an issue with iOS 11.

I DO have an iCloud account that is working just fine.

Device - iPhone X

Version - 11.1.1