On a not dissimilar subject I am travelling alone LHR-PRG on 27 Oct on the BA860. I selected 5A as I like the last row of the CE cabin and have never had anybody in the C seat.
On 2 occasions now I Have been moved to 2A on MMB with seat 5A remaining unoccupied. Also, someone is sitting in 2C. I know the divider can change and indeed it has gone from row 4 to row 5 back to row 4 again bur why the changes.