Help with First Alert Smoke and carbon

I live in the US and I had four First Alert Zcombos connected to my Smart things last year, i put then all up in December and had them all connected to Smartthings. Over the last year my smart things hub has decided to “disconnect” from my router and reconnect. I didn’t think about it until now but my Zcombo’s are not on smartthings any more. Now I go in and tell smart things to add a first alert smoke and carbon monoxide alarm and i hold the test button and push in the batteries like Smartthings says but it never connects to the device, please help!!!

I’ve 5 of the ZCombo alarms, but haven’t had this problem. I looked at the manual and I’d try a reset (see below) then try to re-add.

If the device is powered up with the test button held down for 10+ seconds, the device will reset all Z-Wave settings and leave the network. NOTE: The device will not remain awake after resetting and will go into standby mode.