Have you tried using Hubitat's built-in HomeKit integration?
Have you tried using @dan.t's MakerAPI HomeBridge Plugin? I have been using this for years and it works amazingly well. I like it because there is no custom code required on the Hubitat hub.
Just a couple other ideas for you to try. 
Have you performed the HomeKit architecture upgrade on your iPhone? I have chosen to leave mine at the old version of HomeKit for now. Not sure if performing the upgrade might have anything to do with the "No Response" messages you're seeing.
