To check DFSR backlog, run following commands on one of your DFRS servers.

• dfsrdiag backlog /rgname:<REPLICATION_GROUP_NAME> /rfname:<REPLICATED_FOLDER_NAME> /smem:<SERVER_1> /rmem:<SERVER_2>
• dfsrdiag backlog /rgname:<REPLICATION_GROUP_NAME> /rfname:<REPLICATED_FOLDER_NAME> /smem:<SERVER_2> /rmem:<SERVER_1>

For verbose output, add /v switch at the very end of commands.

Windows Server 2008 R2
Windows Server 2012