CPU Load strange behaviour - video attached

Please see this 30 second video:

I have used Massive X as an example.

Notice that when I have only one track selected in the track list, the CPU performance is quite high. But… if I select all tracks in the project, the CPU load goes down quite a bit.

I’m on Mac Catalina 10.15.4 running Cubase Pro 10.5.12 on an iMac i7 Quad-Core Retina 5K, 27-inch (2017 model).

Just wanted to show what I have found. Surely it shouldn’t matter what tracks are selected, should it? Or what tracks are record-enabled…

So this issue isn’t even platform specific it seems.

I’ve done adequate testing now, and have fully rebuilt my main windows 10 (in my sig) workstation to ensure nothing, not even leftover windows service pack data or migration data, remained.

Cubase does this same thing, and as I’ve watched other users… Select or click MONITOR on tracks and experience drops in cpu, I’ve tested the same and I see the same.

I previously thought ASIO guard was a prime culprit because the issues seemed to respond to guard off/on/lo/med/hi settings. Then over time, the issues came back and I observed they are separate from guard.

Now I have guard disabled entirely, 64bit precision, high cpu priority, and multiprocessing enabled. For me, this works best, along with careful selection of tracks or utilization of the monitor feature in each, and reduces the high cpu peaks to almost nothing.

Other users claim confidently to have resolved the issue entirely by fully disabling hyperthreading for their cpu in their motherboard BIOS. I am not willing to do that other than to observe that it works, as I will not be disabling all 6 of my virtual cores all the time just to work around an issue that was not present… In my last Cubase environment on this same hardware platform.

I eagerly await a patch. From somebody… Either steinberg or Microsoft, in my case. I believe the issue is caused by Microsoft and their changes to multimedia multi-threading rulesets under win10, but… Is this the SAME issue under Mac os? That would be a hell of a thing, lol.