Solved
Update #2: I was wrong. My light groups are still flaky. 
I’m moving this discussion to a new thread with logs. [Solved] Troubleshooting ZHA light group
Update: The problem seems to be resolved after disabling the ZHA group, and the YAML group, and just using the YAML defined Group of lights (group.dining_room_light) instead.
The question still remains, is the ZHA group issue a bug that should reported, or just a quirk with Hue lights?
Today I have tried:
- YAML defined light group
- ZHA defined light group
- YAML defined group of lights (ie.
group.dining_room_light)
When I flip the entity switch in Lovelace, within a second or two the switch flips right back on. Sometimes all of the lights turn back on, sometimes they all stay off. But take a look at the screenshot below. Some report being on and some are off, even though that doesn’t match the physical state.
Now, the group.dining_room_light does seem to work more reliably. But, after being off for 5 minutes, all the lights just turned on at 2% for some reason.
Is this a bug I should report to the ZHA project? Or is there something I need to do differently?
P.S. The YAML light group is disabled. Next I will try disabling the ZHA group.