4/17/15; DM on a FSD-MSP-SLC routing. I boarded in FSD and checked the FlyDelta ap for my upgrade status for the second leg. It advised I was 2 of 32 w/ 6 seats available, roughly T minus 90 minutes.

I arrived in MSP and deplaned with roughly T minus 25 minutes. I checked the FlyDelta ap and found that I had been upgraded from 8A to 1D. I pulled up my new BP showing 1D, pocketed my phone and headed to the gate.

I arrived at the gate at T minus 18 to find most of the passengers had boarded. There was a trio of men around the desk, presumably waiting on standby to clear. I approached the gate agent and she advised that the scanner was down and asked me for my seat number to manually enter me as boarded. I told her 1D and she had a look of disdain on her face and furiously clickity clacked at her keyboard. She replied that 1D wasn't my seat and asked for my name. I gave her my name and she replied that I was in seat 8A. I informed her that I had a BP showing 1D and she said I must be mistaken. I pulled out my BP on my phone and showed her my BP for 1D. All of a sudden she changed her story and remarked that , "oh, you were upgraded to 1D, but there was an emergency situation and I had to move you back to your original seat." It's now T minus 15, so I suck it up and board to 8A. While boarding, I observe a man in 1D and the rest of FC completely full. Meaning there were no broken seats in FC or otherwise.

What possibly could an emergency be to remove me from my FC seat and give it to somebody else? Especially since I presumably wasn't the final upgrade into FC (2 of 32 with 6 open at T minus 90). A Sky Marshall taking that seat due to a risk?

Should I feel slighted by the gate agent's willingness to lie or stretch the truthfulness of her actions until I presented my boarding pass to her, at which she then admitted what she had done to my seat. Should I make any correspondence to Delta after not being served in a class of service for which I had a seat assignment/boarding pass. Long day and missed out on meal service with no chance to get a meal at MSP due to the 25min connection time. What could possibly have been the emergency to replace my seat with another passenger?