Hmmmm, same problem here with a V70 1999. Antenna ring is the main culprit.
I finally cut a spare key and hide it, if the first attempt to start doesn't work, simply swap keys. I have read that too much junk on the key ring MAY
hinder proper operation. My symptons are engine cranks but dies right away, of course all the dash warning lights are lit. Once I tried using same key after a few seconds and everything worked. So go figure. It does this once-twice a month. I have a set of wiring diagrams for this car, Its a worse than a 747.
Anyway WAY more complicated than our 2 122's. Good luck
cheers--