iZotope wrote me back. FYI, I’m on OS X Yosemite and Cubase 8.10.
Thank you for contacting us and I apologize for any difficulty you may be having!
There is an issue with the VST versions of our plug-ins on Mac when using another program that accesses the Mac Accessibility features. This is generally any program that may have it’s own window resizing methods or keyboard shortcuts.
Try opening your Mac System Preferences and clicking on the Security & Privacy page. Then, navigate to the “Privacy” tab and click on the “Accessibility” section. Be sure to disable everything in the list that says “Allow the apps below to control your computer.”
That will most likely stop this problem from occurring. If that does not work, one other thing I would recommend is to again go to the Mac System Preferences and click on the “Keyboard” page. Then navigate to the “Shortcuts” tab and click on the “Accessibility” section.
Try turning off anything checked in this window, especially the “Zoom” shortcuts.
This should clear up the problem! We are working on a fix for this issue at the moment, but unfortunately I am unaware of when exactly any kind of update for this would be out.
I disabled the extensions I had in the “Privacy” tab in the “Accessibility” section one by one, and it looks like extension PopClip (https://pilotmoon.com/popclip/) was the one on my system that did not agree with Trash.
Once I disabled PopClip, iZotope Trash works perfectly in Cubase.