Issue: I am having unpredictable CPU spikes/higher than usual/bouncing CPU and also CPU overload when soloing tracks sometimes, which goes away immediately after de-soloing the track (regardless of what plugins are on it, or whether it’s an instrument or audio track). I’m back on 10.0.4 as 10.5 is now unfortunately unusable for me. All of these projects are 100% fine on 10.0.4.
Repro: Use Cubase 10.5 on a Mac using Mojave. 
Is anyone else experiencing this specific kind of thing on Mac?
Yes I noticed today on 10.5.5 Mac Mojave when using a mixing template that has many busses with plugins, I was bounced down to just 5 audio tracks.
When I solo’d 1 track that was running on an 8 bar loop,it would loop twice and then the performance meter would hit max and no sound would come out. As soon as I de-soled all 5 tracks would play fine!! If I tried soloing another track same thing would happen after 2 cycled loops. Un-soloing would go back to normal. I might have to go back to 10 as this has never happened before.
My situation is exactly the same as yours! Even the latest cubase 10.5.5 hotfix did not fix this problem. It is really very distressing. I can only work with cube10 now.
Are there other Mac users who can confirm this specific issue? This is not the Mac graphics-related issue in another thread – this is specifically for CPU overloads, as detailed above.