Yes I was at a Sheraton (a week before the migration) and cancelled a stay - they couldn't see the cancellation nor the reservation number (although they could see another res number - somehow the system was generating two entirely different numbers). There were a few of these double res numbers - one of which the hotel could not see - even tho it showed up on the app (and IIRC the website)
My stays did post thought. I suspect the res they couldn't find might have something to do with the res I had cancelled on their website but it didn't show up at the hotel (the inverse of your problem) Pretty clear that the migration wasn't entirely successful!