Error 9002. The transaction log for database is full due to AVAILABILITY_REPLICA error message in SQL Server

Error:

The transaction log for database ***** is full due to ‘AVAILABILITY_REPLICA’

Cause:

This occurs when the logged changes at primary replica are not yet hardened on the secondary replica. 

Fix:

Make sure Always On setup is working properly.

Start the SQL services on secondary replica server and resume data movement for the always on availability groups databases. The databases should catch up and after they do and log backups log files will free up space and return to normal.

Sources:

https://support.microsoft.com/en-us/help/2922898/error-9002-the-transaction-log-for-database-full-due-to-availability