My previous clearly shows the sheathed brown in the 2 way position as number 3 and number 3 into the new switch - sadly I used the incorrect image of the wifi switches previosly posted.I did as you said and it didn't power on. However I switched the sheathed brown cable (which on the old switch was in the 2 way terminal) with the other 'i way' brown, the switch now works. So the sheathed brown wire must be the wire coming from the light.
To confirm at the master switch:
L = both solid brown wires from old one way terminal
L1 = Sheathed brown, brown wire which was connected to old 2 way terminal
Comm = isolated
3 neutrals = isolated
Black with brown sheath and grey with brown sheath = both isolated
The light turns on and off with no flicker, but switch 2 is dead
This is what I propose next, if yours have no neutral terminal then keep the WAGO
Make the black safe (I'd habitually put it in with the earth at each end but others opinions differ)
