Hello @James H ,
Please check the following article for potential reasons that would explain the clients expiry license
https://www.bitdefender.com/business/support/en/77211-129487-licensing.html#UUID-19c664b9-07c0-e5c1-ea33-dde9d6d80b42
Ensure that those clients do not have a Subscription End Date set which is reached, the auto-renew option is enabled or any other condition that might be set at the licensing level as per the article shared.
If you still are unable to pin point the route cause, please open a case with our Enterprise Support Team for assistance.
https://www.bitdefender.com/support/contact-us.html?last_page=BusinessCategory
Kind Regards,
Andrei