For databases utilizing Availability Groups. This wait accumulates when the log capture mechanism (used to send/receive changes between primary and secondaries) is synchronizing. Synchronize events typically happen post-failover or after a replica loses connection then comes back online. This is a common wait, small values are acceptable but excessive values should be investigated.
- Check the SQL Server error log for more information
- Examine wait statistics on the instance for other Availability Group issues. Investigate accordingly
AlwaysOn Availability Groups Troubleshooting and Monitoring Guide