If it is the UCM reset you are hitting ( and after certain faults you have to ) and the elevator is faulting out at floor level I would have said a very likely culprit is the brake switches , as they are quite a common fault . However that would not explain why always the top floor ? When the fault happens do you find it bang on floor level at the top ? I'm wondering if you are getting 'roll back ' when trying to go down from the top ? Anyway ...take a look at the logs/ events and that should point us in the right direction .