Very puzzling that the gap between the guide blade assembly and the DPR hatch is so large... I can see that the front axle would coincide with the hatch if it was further forward... but a betterdesign solution for compatibiity with the ARC PRO would, in my opinion, have been a split axle approach as used in the BMC minis.
To confirm this diagnosis, you could run the car by hand across the start line (and remember you need to cross the exit sensor too).
Then, temporarily extend the length of the blade using black pvc tape... and try again. The test here is bringing the rear edge of the blade closer to the IR LED... thereby improving the dual triggering of the lap sensor configuration.