Many iPhone X users are facing issue with lost notification when unlocked the phone using FaceID. When get a mail notification, and pick up the phone and look at the phone, you can see the notifications reveal themselves, and then immediately disappear (as if users have dismissed them).
The issue is faced only for Mail notifications, the others apps notification apps like Whatsapp etc. stay on the screen. Not only iPhone X but also iPhone 6s/ Iphone 7 are facing this issue. When e mail notification is received user Picked up the phone and the notification vanishes. The issue is very frustrating as you may miss some important mails. Interstingly this is reported by some users only happens with Exchange email but not iCloud email. Gmail on IMAP works correctly.
Fix for iPhone X Email Notifications Cleared from Lock Screen When Unlocked using FaceID
Fix 1 : Turn on Show in history
One working solution found for this issue is to change mail setting.
Goto->Settings > Notifications > Mail
For each account, uncheck "Show in History"
Let me know if that fixes it for you too.
Fix 2: Re-add exchange server
Since the issue is reported with iPhone X and exchange server mails it seems that removing and adding the respective exchange account helps.
Fix 3 : Lock screen notification
Turn the below setting to see if it helps in mail notification issue:
Setting>mail>notification>Each mail account you have to Turn on Show on Lock Screen.