I think you may have recovered the aircraft OK but when you get time back at base you should dig a bit further.
I would be checking the condition of your earth points in the area of the tailboom. Notorious spot for corrosion and often not obvious.
Sounds like you may have had a weak ground for the relay and it not pulling in hard enough due low voltage - hence the noise in the headset of the contacts doing a bit of casual "welding" with the net result it welded closed?