Honeywell Lyric T5 thermostat showing “No Response” in Apple’s Home app.

My Honeywell Lyric T5 (RCHT8610WF2006) thermostat, that otherwise looks and works great usually can’t be controlled by and shows "No Response" in Apple’s Home App. 

Having tried many things, one combination restored proper operation for something under a day, i.e. I removed the thermostat from Home app. and cycled my iPhone off then on, then re-setup thermostat using iPhone 8+, scanning HomeKit label.