I’m having the same issue.
I’m a newbie at Cubase and was working on my first actual session a couple of days ago when this happened. I was running Cubase Pro 8.5.30 on macOS Sierra 10.12.6. So I thought to myself, maybe they fixed this in Cubase 9.5… So that gave me the final push to make a clean install of my Mac and try Cubase Pro 9.5, that way maybe I’d buy the upgrade at the end of the trial, but this time I’m running it (9.5.10) on Mavericks 10.9.5 which is unsupported, but it seemed that many people running Cubase 9.0 were having less issues on Mavericks to begin with, and Mavericks is just much faster than the newer OSs.
Results: It’s happening in Cubase 9.5.10 as well.
Since I’m using presets, I found that simply re-choosing the presets corrected the issue (instead of completely removing the instrument from the slot).
Apparently this doesn’t affect Prologue. It does affect Spector a little bit but Mystic a lot! Like the OP said, something that seems like it would ruin your monitors.
Funny, I try to move to Cubase after getting aggressive loud noises with Pro Tools 12.8.3, only to get these issues with Cubase now…
Is it possible that Steinberg hasn’t noticed this issue yet even though it’s present in Cubase 8.5, 9 and 9.5???
UPDATE: I completely uninstalled Cubase Pro 9.5 (even removed the receipts) and installed Cubase Pro 8. The issue is present there as well.
Honestly, is it possible that Steinberg actually missed this, or even worse, don’t even want to fix it??