My meetings - list of meetings has disappeared!

Students in an online course book meetings with me. They show up in My meetings and I am the host.   But now they have disappeared!   Can anyone tell me how to get them back?

The system for booking meetings (Calendly) also sends a meeting invitation to outlook, so I have the meeting number and link.  When I click the link, the zoom meeting workplace window opens with the message 'Invalid meeting ID'.

What do I need to do to get these meetings recognized as valid meetings and  back on my list ?