My understanding of that dangling pointer error is that it's typically a symptom of a vehicle missing from the traffic storage. That doesn't seem to be the case here, it may be due to the trailer hookup.
I do see that D.B Creation Traffic Vehicle Definitions has a separate file for the Range Rover variant with a trailer, whereas in the base game it's included in range_rover.sui for easier maintenance.
There may be some possible solutions:
Solution 1: Remove or comment out range_rover_hk.sui from traffic_storage_truck_light.db.sii in the D.B Creation Traffic Vehicle Definitions mod.
Solution 2: In the D.B Creation Traffic Vehicle Definitions mod, merge the Range Rover with the trailer hookup into range_rover.sui like it is in the base game.
Feel free to let the mod author know if these solutions would work!
Of course, if you have a sound mod that changes the air brake sounds it may be overwritten.