LZW31-SN - Not responding to commands

I have a Red Series dimmer switch with no neutral installed in a three way setup (aux switch) for controlling a hall light. The switch is connected to Smartthings - using the classic app - and it has been working well for over a month.

I can manually shut the light on and off with no problem but have lost the capability to turn it on and off or dim it through smartthings and or google home. Have read through a number of posts but can not find a specific solution to this issue.

If I look in the smartthings IDE I see the following:

Note the status is inactive and the network security level seems odd.

Any suggestions on how to correct and what might have caused this situation

The network security level is fine. They may or may not pair as an S2 in ST.

Inactive means that the switch has lost its connection to the hub. I would try excluding it from ST, then re-add. Or exclude and factory reset the switch, then re-add.