How long were you holding the key in the "start" position? Solenoid contacts easily overheat and weld themselves together if left "on" for too long.
It was only a few seconds, five at most. When I hear it turn slowly, I try to stop and try again to see if it's still slow, which is what I did.
I had just finished the long tuning process. The starter was certainly warm. Maybe natural cooling freed it or maybe the hammer.
No chance it's the ignition switch, right?
