Yeah, so, I’ve had this happen with a Zwift update on ATV and my Tacx NEO 2T.
UN-install Zwift on the AppleTV. Ensure the NEO (or whatever trainer you’re using) is NOT paired (in ATV Bluetooth device settings), then restart the ATV. Reinstall Zwift, log back into the app and try again.
Failing that, do a RESET of the AppleTV (restore to factory settings). Restoring it will be easy since you have an iPad. Ensure the operating system updates, post reset, then reinstall Zwift. That will almost positively fix it if option 1 above doesn’t.
Finally, for future: always, always, always force-quit the Zwift app on ATV after use. You technically shouldn’t have to but that’s not the reality we live in - force-closing it seems to prevent a tonne of issues.
EDIT - note that the above has worked for people with other brands of trainer as well: Zwift no longer sees Kickr V5 (via Apple TV)