That’s the main issue, but I think your suggestion to look in the hue app and change the behavior of stop sync is going to be the final solution. But the reason calling “turn light off” doesn’t work is because, even while the sync box is working and the lights are syncing, the state of the lights reported to Home Assistant is “off”. So when I call “turn light off” immediately after syncing stops, the service just tells a light which is in an off state to turn off, which does nothing.
If you look at the screenshot above you can kinda see the order of operations that happens after syncing stops. The sync box is turned off, my switch turns off because the box powers off, three seconds pass, and then the light turns to an “on” state from an “off” state.
I can look into saying something to hue about the syncing, but they don’t seem keen on keeping the device up to date. HDMI 2.1 would be much more welcome.