Is there a fixed limit on the maximum number of cluster interfaces that can be QoS enabled in a Smart Center Server on R77?

We have approximately 300 clusters and each cluster has the external interfaces enabled for inbound and outbound rates. We have hit an unknown limit it seems with the policy pushes on the SMS server to the clusters individually reporting "QoS policy , Floodgate Blade - Error: Has more interfaces than supported by fg".

All the clustered gateways are running R77.10.

Many thanks in advance.