Criteria for Avamar replication to remain in queued state?

Running into an issue with a customer who needs multiple replication policies in order to replicate clients in a timely manner. Have separated the clients between multiple replication policies and no clients are being duplicated. Also staggering the start times of the replication policies so that all of the "accounting/housekeeping" that occurs at the start of a replication job can complete in a timely manner before the next replication job starts. Have previously been able to have 4x replication policies eventually run concurrently (after staging the start times) with a total of 28 clients replicating. However, recently only the first 3x policies are able to begin the actual replication of clients (20 clients) and the 4th policy just sits in the "Waiting - queued" state, and so far has done so for its entire schedule window, eventually failing with "Timed Out - Start". Trying to figure out what could be causing this now after it had been working for some time. Looking for some insight as to what aspect of Avamar could be causing the replication to queue when it has not been doing so before. Avamar version is v7.5.1-101, FWIW, and Avamar is integrated with Data Domain running v6.1.0.21-579789 DDOS. All comments/feedback appreciated - thanks.