Simply not true. It happened. This is being pushed, along with the fake “secret deep cover” agent in russia close to putin. All standard cover your lying a@@ methodology.
The “source” here is a fraud working to steer the media- once again. Barr will KNOW if there is any such situation— top clearance, and Trump already does know. Pretty ham handed “source” leaked to the Examiner (a never trump editor btw).
Some can have their access revoked, while they still maintain their clearance on paper.
Formally revoking the clearance is kind of a disciplinary action - something that has to be done for cause, and can be appealed - like reducing someone’s rank.
Cutting off their access (especially to higher classification levels/compartments) is a much simpler administrative/operational procedure. Once they leave their position, they no longer have a need to know - read them out, cancel their account, take back the keys, change the combinations - just like they do to regular employees who leave. Allowing continued access to classified systems and information is a perk afforded to top people. The President can revoke that with a verbal command.