Just for your info so you can perhaps catch it in case it ever happens to you again.
I think trouble we were having with Zoom when sharing is that I had not properly logged out of my own Zoom session on finishing teaching. I think I was so anxious to get on to catching up with other stuff I just clicked 'X' to close the tab … and did actually sign out properly. I think that Zoom will stay signed in for ever pretty much unless one logs out properly. When I opened up a fresh tab and went back to Zoom, it still had me as logged in. So I believe that might well have been what it was.