Interesting.

Similar thing happened to me last summer.

Flying to YVR with my dad- I had booked 62A and B well in advance and this was in place at OLCI.

At bag drop told seats had been changed to 2 X very undesirable ones on LD. Explanation was a configuration of the aircraft change (but wasn't- started as mid J and was still mid J). Then told UD only for golds on this particular flight.

Made a very polite but determined fuss. At boarding seats changed back to 61J and K. Think the people in those seats were UG to first as they popped up to visit their teenage kids in 60J K wearing F pyjamas.

I was quite happy with the final arrangement- but strange thing was, 62 A and B (our original seats) were empty until about 15 mins after take off. At this point 2 people were quietly taken up to them from downstairs. Not quite sure what that was about.

Bottom line is that a polite fuss does seem to reap benefits in this scenario.