Let me start by saying I don’t have any SMCO410 detectors.
I currently have 3 ZCombos of various vintages. 2 of my 3 ZCombos are connected using ZWAVE_S2_AUTHENTICATED and are working with the “Z-Wave Smoke Alarm-Mc” driver, so I don’t think S2 security is the problem.
What version ST hub do you have?
I have a number of the first Gen ZCombo’s that work fine. They do not support S2 though. I only mention a potential S2 issue because that is the step these seem to freeze up on during pairing.
I have both a v2 hub and a v3 hub at my primary location, my security devices are connected to my v2 hub. The issue with the “offline” messages from my remote locations has resolved itself in the last couple of weeks. I just added another ZWave Combo Gen2 smoke/co detector to my 3rd location where I only have a v3 (Aeotec) hub.
Thanks for responding! To save everyone time, it appears that you need a v3 hub for the SMC0410.