Were you possibly moved to/from a reconfigured 321 to a non-reconfigured 321 or to/from a LUS 321 to a LAA 321? Excluding the A321Ts, there are 3 different 321 configs flying: LAA, LUS-original, LUS-reconfigured. And, soon a 4th of LAA-reconfigured. Until the fleet is done (by 2021 I think), seat changes are going to be a potential issue during last minute equipment swaps.
And then of course the A321neos, but I'm not sure if those seat configs are the same as the reconfigured LUS aircraft.