This sounds like a problem I had with a lie flat seat on one of the refurbished 777-200s. It was one of the Super Diamond Solo ones. I first tried to use the button that should have made the seat go fully flat . It did not. The leg rest section stopped short which left a gap. I checked for interference but there was none. I then used the button to adjust the leg rest all the way up. The seat went fully flat after that.