Realtime-Peaks under El Capitan / Macpro


on my MacPro I have two identically configured systems, one under MacOs 10.9.5 (Mavericks) and one under 10.11.8 (El Captain.
But under El Capitan I have MUCH more and heavier realtimepeaks than under Mavericks.
As I said EVERYTHING is configured identically, same software (Cubase 8.5.20), same RME Drivers, same Plugins.

The problem appears especially, when i activate any audiochannel input monitor.

Does anybody know that problem, and what can I do?

Regards, Arno