I too can execute Siri off/on commands (to Generic Z-wave dimmers and Zigbee Bulbs) via Apple HomeKit which update the Home app as well as the actual devices attached to Hubitat.
When I execute a Siri setLevel command to HomeKit (which updates the Home app, it doesn't update the Hubitat devices.
When I execute a setLevel command via the Home app, it does update the Hubitat device.
Yeah, I noticed this was an old thread, but hoping someone (like yourself) would respond!
I'm using the HomeKit Integration. Thanks for pointing me to the "HomeKit dimmer switches" thread. I did a search for "Siri" as that's the main problem for me, so that's why I didn't find the newer thread.