Losing all webinar contacts

I had a webinar set up and many people registered. The zoom interface to sign up is very boring, so I switched the registration to Luma, with the Zoom integration. So that people don’t have to register in 2 places, I turned off the Zoom setting “Registration Required.” But then it permanently deleted all the email addresses who signed up on Zoom. 

Reversing that setting change doesn’t do anything. Very bad design.