Red series on/off. Strange wiring?

I attempted to install a Red Series on/off switch in what appears to be a two-way setup. The dumb switch I’m replacing has line, load, ground and a traveler. There are neutral wires but are not used. When I install the smart switch (with a neutral, of course) the smart switch does nothing. The lights won’t turn on and the other dumb switch in the circuit also won’t control the lights. In the box with the smart switch there is another switch that only has a ground wire and a traveler wire, no other wires are connected to it. In the original switch setup, it doesn’t appear that that switch with only the two wires (traveler and ground) connected to it does anything that I can tell.

What might the purpose of that dumb switch with the traveler and ground connected to it be? Any ideas?