Hi Rob,
As Alan says, G-WTSN is NOT a Mode S contact, it is either an ADSB contact, or a P3i contact with a different 'GroupID' to yourself (which wouldn't show the P3i '#' brackets). I would need to see your traffic screen to confirm which.
The 'bearingless' Mode S target - which would have been giving an audio warning from the PAW audio output of 'Traffic Danger' just before the red ring appeared then 'Traffic Alert' just before it changed to 'amber' - indicating that it was moving away from you - clearly has its relative altitude (-1.6) - i.e. 1,600 feet below you in the standard SkyDemon notification position, which is in your 12 o'clock. The problem is that in the current SkyDemon version the text for bearingless targets is currently very 'fine' with no background contrast, which makes it very difficult to see. Lee, myself and others have identified this to SkyDemon and have been working with them to address this issue, as a result of which this problem should be fully addressed in the next SkyDemon release.
Hope this helps clarify the position.
Brinsley,
I think the multiple alerts when multiple devices were connected was probably purely coincidental. The multiple alerts could have been from multiple targets but this can also happen due to varying received signal strength from a bearingless target aircraft - initially causing it to break one of the alert thresholds and trigger an audio alert, then dropping back below the threshold, then rising back through the trigger point again. Unfortunately there is no easy way of preventing repeat alerts in these circumstances, however in practice this usually happens due to local screening - e.g. when the aircraft is in the circuit and the PAW is as in your case stationary on the ground (especially if inside a building). Fortunately it happens fairly infrequently in flight.
Regards
Peter