Originally Posted by
wakesetter93
I'm going to guess that you have upgrades selected for only a certain kind of seat (i.e. Window/Aisle) and the available seats were middle seats. Those are the only cases where I've seen them not process the upgrade. Check your preferences in the Delta app.
It was on a 145 so it was 2X2 and I had both Aisle and Window checked. I was actually surprised that the GA let them go out empty. I figured it may be a Diamond thing. AA used to do that for EXPs. They would actually leave the middle open next to EXP unless it was sold. Figured it may that way on Delta.