I would clean the ground screw anyway, even if that is not the problem here. They have a tendency to get corroded over time. Especially the ones that have limited contact area due to annodizing that covers the top of the post and slightly into the hole.
It does sound a bit like the trigger magnet is adjusted too close to the HES sensor. As mentioned, back it out and see what happens. Then you can readjust it to tune where the activation point is.
Except for the Automag in front, its usually the man behind the equipment that counts.