Sorry again for the confusion. The black dimmer started working again after I wired it in a second circuit. I put it back in its original circuit and it is still working.
However, now the red dimmer that was in the second circuit stopped working correctly in the same way. It seems very similar to this behavior: Dimmer will not turn off . I have now ruled out wiring faults. The dimmer is also not permanently disabled, because the black one started working again. (Unless a fused relay can unfuse itself.)
It seems the issue must be related to either the change from SmartThings to Home Assistant, or the upgrade of the firmware to 1.57 that was initiated by HA.
I tried reinstalling the dimmer, installing it without load first, factory resetting it and turning settings on and off to get it out of its funky state but it has not been successful yet. I’m concerned my other dimmers will display the same behavior when I port them over from ST to HA. Any idea of how I can get the dimmer out of this state? It seems like it has happened with other people before. Thanks so much for your help!