Can’t add an ecobee to HomeKit

One of my ecobee thermostats won’t add to my Home app - it says device not responding, but the device responds just fine to the ecobee app and to Alexa voice commands. I removed it from home app, thinking I should added it anew and start again but now, the ecobee and Home , dont see each other.

my other ecobee thermostats in My Home are all showing up as usual in the home app and I responding as usual