AI Aircraft Landing Short

I am noticing a lot of aircraft landing at YBCG (coolangatta) and landing WAY short of the runway. When I am watching them, they seem to be going fine then all of a sudden they drop to 0 and bounce along the ground all the way to the runway.I am using airport facilitator X to edit my airport files, and in this example, i extended to runway to match the correct length. Have i forgotten something that is causing the planes to land short?CheersBeau