Seaplanes loss of control after hitting collision gizmo or mesh


As we near the completion of our scenery which is a seaplane base in Sydney, AU, there seems to be an odd bug, where no matter which type of collision we apply, the seaplanes such as the beaver, get stuck after hitting the invisible collider. No controls until we slew and place the aircraft on top of the collider, gears automatically extend then we get controls back.

The collision handling is completely off… any suggestions?