When I checked in to a flight this evening I was moved from 6A to a middle seat on the same flight. When I inquired with AS they said it was for someone with a service animal.

I know you can be moved in 6B and C if someone with a disability needs the seats, which I fully understand. However, is it common practice to be moved from 6A for a service animal? It appears AS doesn't view giving me a middle seat as problem. I specifically booked this flight over others because 6A was open.

Also to add to my confusion, someone on the upgrade lists shows being upgraded to 6A?

I am having second thoughts about my loyalty to AS but wanted to make sure I was being fair to AS before deciding if I want to move on.