I think people have had mixed experiences. Some have had the certificate automatically returned to their account. Some have had it completely disappear on them and then its an uphill battle to even get it back since no one really understands them.

The best course of action if you want to cancel or even to change the dates is to first get the certificate DETACHED from your reservation, refresh the app to check that it is actually back in your account while on the phone and then cancel the reservation. This is what I have done a couple of times when making speculative bookings and its always worked for me.