Error messages and resolution
Shared mailboxes are being backed up but are not considered as part of Shared mailbox licenses as Insync is not recognizing the Shared mailboxes attribute.
It is possible that the configuration is not updated, and shared mailboxes are counting under the user licenses, consuming the Insync M365 licenses, so we need to update the M365 Druva settings.
This issue can be resolved by re-authenticating the M365 Druva application used for EXO backups with a Global admin account. It can be an M365 advanced app, M365 basic app or the exchange online sub-app. The reconfiguration will not affect any backups. it just refreshes the config.
Upon re-authentication, you can wait until the next backup finishes so Insync can count the activated shared mailboxes under Shared mailbox licenses.
Post re-authentication of the M365 Druva application, you can manually backup a shared mailbox and see if it is reflected under shared mailbox licensing.
Refer to the steps mentioned in the below KB article to re authenticate the M365 Druva application.