Dec 15 2017
Every so often we receive this warning message when @mentioning a user that has been a member or even a group admin. How recent is 'recently added'? Days, weeks, months?
In all cases the users were actually able to see the post. Just curious how long it takes for a member to update.
Dec 27 2017
This sounds like a bug. I'd suggest providing all the pertinent details to Microsoft via a support ticket.
Dec 28 2017
Thank you @Kevin Crossman - will do! Happy New Year!