I’ve tried a few times on points stays, and it never worked. I made a comment at the front desk the last time I tried, and I was told that the policy was to not issue the mobile key for mobile check-ins on points stays so they could check ID. Not sure how factually true that is, but it would explain my experiences. I’ve stopped bothering in most cases, as the hotels that have keycard readers in the elevators are a PITA with mobile keys.