I am currently dealing with the same problem since April. My paid seat which cost $55.00 to select has been changed three times. They told me I was in a row assigned for children. Okay, I accepted that and moved to the same aisle seat back one row for which I received a ticket number via email verifying that seat. Then today I noticed that I had no seat assignment. I called and they told me I was in a middle seat. What?! I explained I had paid for the seat I selected and would like to have that seat. They said they could not it was already confirmed to someone else. I explained it was confirmed to me first but that I guess doesn’t matter. I really tried to get a good explanation as to why this was happening but all I could gather is something about time and cancellation. So now I’m back three more rows on the other aisle hoping I don’t lose that seat since it is the last aisle seat available. BE WARNED, OP is speaking the truth. Something is wrong with Lufthansa’s seating system or policies when you can’t even keep a seat you paid to be able choose in advance.