Zoom is TOUCHY. Like real touchy. We're working on replacing it with a new system. In the mean time, be sure to follow all of the instructions on the check in form, and if necessary, reschedule a lesson or do a lesson without the stereo audio option. We'll have a more dependable solution soon.
If you're having issues with Cubase on a Windows machine- that is a known issue for versions of Cubase before 10.0.