I had a similar issue. It only happened when it rained. We had a water leak somewhere in the front firewall that leaked rain water into the passenger floorboard and would soak the carpet. The water/moisture caused a short and would open the lift gate. We had the leak sorted out by a body shop and the lift gate never opened on its own again. Not sure this is what’s happening in your situation, but maybe check the passenger floor for any water leaks.

We had that exact issue! We were getting moisture that was triggering the hatch to open. It was wet under the carpet right by the passenger fuse box. Did you pull the panels and carpet back to confirm it’s dry there? We took ours to a body and collision shop. They found a leak under the hood near the passenger firewall that was leaking rain water into the passenger floorboard. Don’t know exactly where they found the leak, but they filled it with silicone (or something) that stopped the leak and the problem never returned. Definitely confirm under the carpet and insulation foam is dry.

I’d say it’s good news that there isn’t water inside the cabin! Another thing to check is the wiring that goes along the floorboards under the plastic panels at the door entry points. You might want to pull the panels back and check for any shorting out wires. Keep the tailgate closed and start gently wiggling any exposed wires and harness’ to see if that triggers the gate to open. The difficult part about this problem is that it’s hard to replicate and trace down. We at least had the leak that was most likely causing the gate to open. Once the water leak was fixed the door functioned normally and never set off the alarm again. Hope you figure out what’s causing it. Good luck!