Hi,
Anyone able to use the basic function of a dependency rollup monitor for a Group With a large number of members?
To represent Exchange end user availability we have put Object of ‘Exchange 2013 service Components’ in a Group and added Performance and availability monitor to this Group. The problem is that it only displays Health state occasionally. Rest of the time it is uninitialised. I believe it has to do With the amount of Objects, in this case 2501 to be exact 
Was doing some searches and actually ran across what may actually be the underlying issue here. When you created the Dependency monitors for the group, did you directly target the Availability and Performance aggregates (as one normally would?).
The reason i ask, is that based on https://blogs.technet.microsoft.com/volkancoskun/2014/10/19/how-to-fix-the-health-rollup-problem-in-distributed-applications-with-exchange-2013-health-sets/ and also a quick check in my own management group, the Exchange Service Component’s only unit monitor is an event monitor that has been set with it’s parent monitor as “Entity Health” directly.
As such, the dependencies are missing the only monitor that is actually generating health for these objects. The article proposes that you duplicate the monitoring, but for your purposes it may instead be easier to use the SCOM console to create a Dependency monitor that just rolls the top level Entity health of the service component up into Availability directly.
that is a great find - i didnt make the Connection With Exchange. As you assumed. the dependency rollups ar set at Performance and availability. I will try to change this later today and report back.