Newly installed dimmer switch doesn't power off
This dimmer's instructions endorse the idea of just capping off the ground wire if the switch outlet has no access to ground.  However it also requires non-metallic faceplate and also non-metallic faceplate screws, so you'll need to take care of that.
That means this dimmer is NOT a modern type (those either need neutral to power themselves, or a special UL variance to bootleg ground as neutral. Those won't work without ground, but that is not your dimmer, so not your problem).  What you have here is the &quot;old school&quot; classic dimmer that powers itself by leaking power through the [incandescent] bulb. Only certain LEDs will tolerate this; the rest need the modern dimmer type that self-powers.
Lutron has a list of recommend LED bulbs; a few bulbs from Commercial Electric are on it. This one is not.
I would start by rolling it back to incandescent (or just temporarily hooking up an incandescent light for testing purposes).  If the dimmer now works properly, you know the dimmer is reliable.
Next, I would try temporarily wiring up BOTH the incandescent and the LED fixture.  This is a trick we use a lot for diagnosis.  Now, see if the LED fixture dims correctly with the incandescent in parallel with it.
If it does, then the dimmer is using the traditional strategy of leaking current &quot;through the bulb&quot; to power itself.  Of course you can't very well go leaving an incandescent bulb in your lighting; those things burn out! And when they do, your LED will be back to the bad behavior, and it won't be obvious why.  Lutron actually has an answer for that; the &quot;LUT-MLC&quot; incandescent bulb simulator module.  This can be wired in parallel with the LED and left up in the junction box.