User ID keeps defaulting to Email

Hey Everyone,

Wanted to see if anyone else has ran into this issue where a rare select few users are showing up as their email instead of their full name? I'm going through my users for scheduling purposes and would like each users to be displayed as Full Name, All users have been able to display as a full name besides 3 that will always revert back to email display as the user id... No matter what I do, delete them, re add them, anything. 

Anyone know of a fix for this? Very annoying as all others were easy updating their info and having their full name display as the User ID.

Thanks,
Alex

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Alex Bennett
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