I just get so stressed when I see anything about plane seat issues - everyone is all "you should pay" but it doesn't take into account all the things that can go wrong, and there is now zero compassion or willingness to shift from other passengers. And somewhat reasonably, as they have paid for their seats!
I'm still traumatised from 6-leg (3 each way) flight last year with DH and then-10yo DD, where despite paying close to £1K to select seats (for very tall DH to get extra legroom and make sure the family was sat together), we sat together on only 1 of the 6 legs. First leg was fine. Second leg - long haul - 2 of the 3 seats we had booked were literally broken and NO ONE could sit there. It took ages for the flight attendants to find anyone willing to move to allow me and DD to sit next to each other for the 8-hour flight. DD (probably ND, we're looking into it), not having flown since she was 4 before the pandemic, was in tears and terrified. At least DH got his extra legroom in the non-broken original seat. Then, that flight encountered weather and we missed the connection. So obviously we didn't have the seats we had paid for on the flight that left before we got off the plane. Again, massive difficulty to find anywhere to get even two seats together. I managed to get behind DD (aisle seats - yet the middles next to us didn't want to move to an aisle to allow us to sit together - I have actually seen threads from people explaining that they chose such on purpose...). Return journey they had overbooked the plane and printed boarding passes with our seats for multiple people. Again, lots of angst but we got DD and me next to each other (and DD absolutely in a panic remembering the problems on the flight over, and me not so far behind). Weather again, and despite actually making the connection, we got there so late they had removed our seats from the system and put other people in them. This time DH was crunched in a regular seat and we did manage to get me and DD together in some middle seats. Final leg the plane was a different type than planned, so at least nobody had seats they had booked, although people still insisted on their seat if they existed in this plane. Again, couldn't get three together and lots of difficulty over arranging for me and DD together. Didn't help that DD was a very tall 10yo (see tall DH...) and people seemed to think she was a stroppy teen and not a panicking possibly-ND 10yo at the end of a very long series of flights.
I'm grateful that I managed to get next to DD on all but one of the legs, but it was so incredibly stressful that I have a panic response at the thought of flying long-haul again, making me really not want to visit family overseas anytime soon...
I completely understand that people don't want to give up seats they may have paid £100+ for. But the fact that everybody pays for very specific seats now means that the gate staff can't shift people who haven't yet checked in around (while keeping groups together) like they used to, to help sort out groups broken up for various reasons. And there is no sympathy because "you should have paid" even when you DID pay (a lot!).
I wonder if instead of picking specific seats, you could pay for "3 seats together with extra legroom", "an aisle seat in cheap economy", etc. I guess that would be much harder for the airlines to sort and figure out if they even could sell that combination, instead of just showing the little maps you select from.