I went back and looked at the history of Tim's Kingfisher at Flightsim. Hard to believe it was originally posted as an FS9 model in 2005. Time has flown so I must be having fun. It did not have a beaching gear at that point. The beaching gear mod was added by Tim himself some time later. Some of the latest files say it is for FS9/FSX. I don't see that Tim did any mods specifically for FSX so I assume these just have the necessary changes to the texture formats. Several of the repaints include changes to the aircraft.cfg file and .air file. I haven't looked to see if the contact points have been changed.
Claudius24, on further review of your video, I agree with Larry, you have a contact point problem. I also run it in FSX with no problem. Here are the contact points from my copy:
[contact_points]
max_number_of_points =16
gear_system_type=2
static_pitch= 5.000
static_cg_height= 5.300
tailwheel_lock=0
point.0= 1, -14.414, 0.000, -6.880, 1800, 0, 0.600, 45.000, 0.250, 1.500, 0.900, 1.000, 1.000, 0, 200.0, 250.0
point.1= 1, 0.667, -2.050, -8.600, 2000, 1, 1.000, 0.000, 0.250, 2.500, 0.800, 1.000, 1.000, 2, 200.0, 250.0
point.2= 1, 0.667, 2.050, -8.600, 2000, 2, 1.000, 0.000, 0.250, 2.500, 0.800, 1.000, 1.000, 3, 200.0, 250.0
point.3= 4, 6.000, 1.448, -7.250, 2000, 0, 0.000, 0.000, 0.900, 2.501, 0.850, 0.000, 0.000, 0
point.4= 4, 6.000, -1.448, -7.250, 2000, 0, 0.000, 0.000, 0.900, 2.501, 0.850, 0.000, 0.000, 0
point.5= 4, -11.721, 1.400, -6.219, 2000, 0, 0.000, 0.000, 0.900, 2.501, 0.850, 0.000, 0.000, 0
point.6= 4, -11.721, -1.400, -6.219, 2000, 0, 0.000, 0.000, 0.900, 2.501, 0.850, 0.000, 0.000, 0
point.7= 4, 0.021, -14.288, -5.437, 1575, 0, 0.000, 0.000, 0.800, 2.501, 0.850, 0.000, 0.000, 0
point.8= 4, 0.021, 14.288, -5.437, 1575, 0, 0.000, 0.000, 0.800, 2.501, 0.850, 0.000, 0.000, 0
point.9= 2, 0.000, -17.908, 0.841, 1200, 0, 0.000, 0.000, 0.000, 0.000, 0.000, 0.000, 0.000, 0
point.10= 2, 0.000, 17.908, 0.946, 1200, 0, 0.000, 0.000, 0.000, 0.000, 0.000, 0.000, 0.000, 0
point.11= 2, -16.699, 0.000, -0.766, 2400, 0, 0.000, 0.000, 0.000, 0.000, 0.000, 0.000, 0.000, 0
point.12= 2, 8.342, 0.000, -3.063, 1200, 0, 0.000, 0.000, 0.000, 0.000, 0.000, 0.000, 0.000, 0
point.13= 5, -14.775, 0.000, -6.056, 2000, 0, 0.500, 45.000, 0.000, 0.000, 1.000, 1.000, 1.000, 0
point.14= 2, 10.000, 0.000, 0.000, 2500, 0, 0.000, 20.000, 0.000, 0.000, 1.000, 0.000, 0.000, 0
point.15= 2, -25.000, 0.000, 1.800, 2500, 0, 0.000, 20.000, 0.000, 0.000, 1.000, 0.000, 0.000, 0
If these don't work for you then there is something else different with your system.
Best, Paul