Funny you should ask. This just happened to us.
We were supposed to arrive on Sept 18th. Last minute travel issues forced us to arrive on Sept 19th. I had completed the online check-in and requested room # sent to me.
While I knew I would not be there at 4PM on the 18th I checked my email often from 4PM but never received a notice that our room was ready. I found this very odd.
On Sunday, the 19th, our revised travel day I checked the My DisneyExperience app and still, no room number was given, and no email saying our room is ready. I just figured it was a glitch with the app.
So when we arrived at about 6pm on the 19th, and still no room number I had to go to the front desk upon arrival.
She couldn't find our reservation at first and then advised that it had been cancelled because we didn't check in.
I was NOT happy. This is/was a two-week vacation, I used my
DVC points to make this reservation and I expected the room would be there whenever I arrived. The lady at the reservation desk was eventually able to get us a room but not a great way to start our vacation.
Our room is at the Beach Club, and I thought all the DVC rooms here have been updated with renovations but the one we are in is a bit tired, and has not been renovated. Maybe a room they have set aside for such problems?