When that zone is watering and you cannot stop it with your Netro app, please unplug the power adapter of Netro controller, see if the zone is still watering. If unplug the power adapter, the zone is still watering, this zone valve need to be checked.
You can also switch this issue zone wire with other good zone wire. For example, assume the issue zone is zone 1, zone 2 is good zone. Switch zone 1 wire to zone 2, and zone 2 wire to zone 1. Test the two zones, see if the physical issue zone still faulty.