Jumper tailgate sensor fault

Hall sensors can be tricky. Did you check the cable and plug connections to the sensor itself? A bad connection there can cause weirdness with automatic tailgates.

I gave them a once-over, but maybe not thoroughly enough. Any tips on what I should be looking for? Is there any specific way to test the connection, or am I just visually inspecting it for corrosion or damage?

Visually is a good start, looking for frayed wires or corroded pins. Beyond that, without proper tools, you're limited. The best bet is probably to get it checked out at a workshop. They should be able to pinpoint the problem.

The connection was the problem. A local shop found a faulty plug and replaced it. The tailgate is working perfectly again. Cost me 95€, sensor fault fixed!