Hello and welcome !

I had the same with my Golf GTi. The problem was that the whole unit shifted somehow. I still don't know how it's possible, but instead of directing 12V's through the wire for the starting engine, it was directing it through the mass! Very weird and I think you have something that is close to my problem. Try to measure some value's in the cables! Note that the key was turning fine, you couldn't feel that anything might have been wrong, just a part or maybe the whole unit shifted, so the contact points didn't match with the original anymore.

My fix: I just changed the cables to their correct value, not looking at the position, just give every cable a place where it can fulfill their function compared to the position of your key!

Greetings!