I've been looking at my reservations for upcoming trips to see if lower rates become available. I have already re-booked three times and saved money each time. Today I am checking again and found it quite strange that I find a non-refundable rate for a few minutes and then it's gone only to find it return again a few minutes later.
Then this rate shows up for the same dates then 15 minutes later it comes back to the rate above.
This has happened about four different times today so I don't believe it is the actual inventory of the property that keeps coming and going, but more another of the famous Marriott IT issues.