Originally Posted by
malgudi
I was assigned a new seat when I scanned the boarding pass, but since my original seat wasn't occupied after all the passengers had boarded ... the purser was happy to let me have the seat back.
Any idea what might've caused this?

Usually they state aircraft change, which in most cases is a complete load of nonsense.
I have been moved from 1A when the aircraft "changed" from an A321 to another A321 ... Both of course have a seat 1A.