Answering my own question...
When a registered device, such as an AppleTV, connects to the network for the first time after registration, Airgroup will create a new Server Entry on the controller. Since it is new, it will send a request to CPPM (hits
AirGroup Authorization service) to pull back and cache the details for the device. Clearpass will return the list of shared users, groups etc.
That entry on the controller does not get refreshed until the "CPPM Server Query Interval" as defined in the Airgroup configuration which by default is 10 hours. This default can be changed. So if a new user is added to the shared list, the controller will not learn this until after the cache period is expired.
show airgroup cppm-server query-interval
You can manually clear the device from the controller. Next time it connects, it will pull CPPM again for the shared list.
clear airgroup server aa:bb:cc:dd:ee:ff
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Philip Wightman, ACEX (AMFX) #69. Aruba Partner Ambassador
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