If you did not register your YogaEasy membership using your original e-mail address, but via Apple access (Apple ID), then your so-called Apple Relay address was created for YogaEasy. These encrypted addresses always end with "@privaterelay.appleid.com."
In this case, log in via "Sign in with Apple" in the app or on the web.
You can learn more about the Apple Relay address here: Information about Apple Relay addresses