@Pierre-Alain_Isore. Same instance here - at least for the First Alert Smoke Detector and Carbon Monoxide Alarms (ZCOMBO). I have two that show offline. I’ve “rebooted” them and they still disconnect after the reboot. Perhaps I will remove them from my list of devices and then try to reconnect them and then go through the PAIN of editing my automation to re-add them. UGH.
Try reaching out to the manufacturer support instead of SmartThings. SmartThings support are slammed right now triaging all the issues they’ve created with the forced migration, and the manufacturers should know their own products better anyway.