Digital Check In not Honored?

I’m a big proponent of digital check in because I prefer the top floor and away from the elevator due to noise levels. The past couple times I’ve done the digital check in and selected my room, when I arrive I’m assigned a different room. What gives?

For what it’s worth, I am a diamond member and do 30+ stays per year for work. Why would they assign me a different room than the one I selected in digital check in? Thanks!