I just installed a HS200 smart switch for the first time today. The switch is used for a front porch light and two garage lights. Mid-80s house and this junction box is on an exterior wall. It seems like a plastic box with a metal bracket/metal screws inside and metal at the top holding the romex in place. The grounds were all clamped together and the excess cut off. There was a second (3-way) switch in the box which is no longer in use, so that is most of the extra wires. I get the exact same result with the ground connected or disconnected.

Issue: When screwing the bottom screw into the box there is an exact point at which the switch will turn off. It is getting tight at this point but I can still wiggle it back and forth a little. There is exposed metal on the back of this switch behind that screw terminal, is this for trying to get a ground from the box? If it is not that metal it is possible my uneven wall and box is flexing the unit too much? No matter how hard I press the bottom against the wall I can't recreate this without the screw.

I tested the live wire in the box using the bare copper ground in there and the reading is 120v. I don't know what other tests would be useful.

Hopefully you will just tell me to put down the drill and pick up the screwdriver next time. Thanks