Originally Posted by
abat
I've found that it matters when you do the online check-in. If you try immediately the check-in period opens my experience is you don't get upgraded. Trying much later (like the morning of the day of arrival) often shows me only one room available in the app, an upgrade, which presumably has been pre-allocated by someone at the hotel.
This is exactly my experience. There is almost always a selection of standard rooms if I check-in online when prompted by the app, waiting until the day of arrival always yields a better selection.