Unlike a lot of services, the Call Log indicates that calls that have come into the Webex Calling system, not just the ones that were delivered to your phone if the phone or app was not registered at the time,
That said, calls should come into your app and/or phone if they are registered and another feature isn't taking over, like if you had your Call Forwarding or Voicemail settings configured to not ring the phone. My guess is that there is something "intercepting" the call before it rings your devices. If you can't figure it out from your Call Settings (in the app), then opening a support case would probably be the best option.
