Some time hours after the car is parked and locked, the whole car unlocks
on its own. Any ideas?

I pulled the fuse for the security system, did not help.

Check every door. Make sure each turns on the dome light. Vacuum motor for each door have switches on them to show the state of each door if one shows open when closed. I would test all of this with the Mercedes tester for any codes as the OBDII tester may not show any codes..

Martin