Its alive!

Turned out to be something super simple.
The positive battery bolt was tight when I checked it, but 2ned time around when I REALLY checked it, it was tight because the bolt was hitting the back of the battery terminal.
It was still allowing the bike battery lead to move a little against the terminal, that was enough to cause it to ‘crack’ when I hit the starter and stop the bike from starting.

I removed the bolt and replaced it with a shorter one, and away we went.

So, while the fix was simple, the lesson learned was not.