I had taken the mention of something breaking on the mower yesterday as part of the tractor package, as well. But maybe that was unfair.
Hopefully it's just a loose wiring connection somewhere in the system, but your mention of it being pretty consistent only after warmed up makes me think it might be more likely a cracked wire in a potted coil assembly (solenoid).
You'd expect loose wiring connection issues to be more random prior to eventual complete and permanent failure. Usually when you see something that fails to actuate only when warm (or only when cold), it's in a potted assembly or circuit board, where CTE is causing a connection to make or break with temperature.