I read in some of the comments in Marriott Facebook groups that there is an unpublished and maybe temporary attribute for Titanium's and above that there is flexibility in the cancelling reservations policy. Quoted here:
"I wanted to book a prepaid rate at the Arts in Barcelona for a 7 day stay in December, I was looking to see if I could cancel if my BA flight is cancelled due to their upcoming and usually long lasting strike. The hotel said no, but when I spoke and booked it with CSR (name replaced) she advised that due to my status Titanium it’s one of the perks, I can cancel the prepaid for any reason and it’s ok.
I was surprised but I must say pleasantly. I never knew this. Anyone else know?"