Grandpa'* car, 62k miles, have my kid driving it. Random non starting over the winter. Seemed to do it less when it warmed up.
Battery Always had plenty of juice, lights on bright, windows up & down.
Alternator was fine
Mechanic Replaced battery over my objection. No improvement.
Still happening, so I replaced starter.
Still happening, Checked all the connections, no corrosion seen anywhere.
Finally had a process that seemed to work : opened hood, jiggled the fusebox. Usually started right away.
Decided to start replacing ignition relays one by one. Still happening, but less often.
Changed out the actual ignition switch, happens less, but still about once a week.
Any more ideas?

if jiggling it does something really the problem must be in that area, either the relay sockets have some corrosion or loose connection or the wires are loose