Can't start meeting - keep getting "meeting ended by host"

I have a Pro account and use Zoom for teaching music lessons online. Today I am suddenly unable to start some of my recurring meetings .... when I click "Start" I get a pop-up error saying "this meeting has been ended by the host".

I am able to start a few of my scheduled meetings and not others.

Zoom also allows me to start an instant meeting using my personal meeting ID, but that's not much good to me in this situation.