Has anyone successfully redeemed a Marriott free night certificate at SPG hotels since the merger?

When searching for rooms, the website has a message to book by phone when using free night certs at SPG hotels. I called the SPG hotline as indicated (twice), but the agents were unable to use the cert. Is this a systems issue or is it just that the agent doesn't know what to do? I'm not sure if calling back and trying again will work. If the former, I'm hoping that this problem doesn't last too long as my stay is coming up.

The agent referred me to status.marriott.com, but the website says systems are online and doesn't give any indication that the free certs can't be redeemed. Not helpful at all.