Avamar Exchange 2013 DAG backup fails – Waiting for VSS

Today I have been troubleshooting Avamar backups of an Exchange 2013 DAG (Database Availability Groups) setup. The Avamar job would start but no data would be backed up and the job would fail within 15 minutes. Initially VSS was suspected to be the culprit but additional troubleshooting revealed some strange behavior of the Avamar client in which the individual plugins would keep waiting for a status message that would never arrive.

The setup is simple: three Windows 2008 R2 SP1 servers, Exchange 2013 Update 5 with Database Availability Groups and Avamar 7.0.2 as the backup software and target. The error that pops up looks like this:

Avamar Exchange 2013 DAG error

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