Thanks Frank 
Well, I can only assume it’s defective as I changed nothing other than the relay itself and then all worked as it should 
I have the same wiring. I am stuck with the line (in) at the bottom of the stairs with switch 1, the load (out) at the top of the stairs with switch 2 and the light in the ceiling at the top of the stairs with a 14-3 (b/w/r/g) cable between 1 and 2. I have no way of installing another conductor to get the line (in) to the top of the stairs. Would it work to convert the two 3-way switches into single-pole, “steal” the traveler (red) wire and make it hot to the top of the stairs, tie the red to Sonoff L in, and to the switch 2 line and connect load to Sonoff S2, use black wire at switch 1 as load to top of stairs into Sonoff S1, and then the black to the load (out) into Sonoff L out? Or does that create an overload problem with potential fire hazard?
