I’m having same issue with 10.5 as I had with 10.0.5 that made me go back to 10.0.4. Cubase is spiking with nothing much really going on in the session.
What changed from 10.0.4 to 10.0.5?
I’m on 2009 Mac Pro high Sierra 48 gigs of ram. 8 core.
Seems like 10.04 is last version usable for me.