We have the same Failover Clustering problem on multiple servers. We escalated to Microsoft and they found a similar case. We have Avamar for Windows version 7.0.101.61 installed on our Windows 2012 R2 server that have Exchange 2013 installed.  We notice if the Backup Agent is running, and there is an interruption in network connectivity, the node drops out of the cluster and then is not able to rejoin.  If the Backup Agent is not running, this does not happen.  Also, when it happens, if we stop the Backup Agent, it is able to rejoin the cluster. Here is the description.  When the cluster service starts, it looks for the C:\clusterStorage folder.  By default it has full access to this folder.  It attempts to create the hidden share CSV$ regardless if shared storage is configured or not.  Exchange does not use shared storage.  The Avamar client blocks the ability to write to the folder which prevents the cluster service from completing its startup sequence.  The reason a reboot fixes this is because the cluster service has a higher priority in the services so that the Avamar service launches after the cluster service has already started successfully. Has anyone run into this and what is the workaround?