Why is every second breaker out in my panel?
Multiple possibilities.

If you have aluminum feeder wire, check the clamp to that wire AND that anti-oxidation compound was used.  As the load varies, the joint heats up and cools down.  Aluminum expands and contracts more than the other metals, so the wire will squish down and work its way loose!  This happened at our old place.  The panel got hot and I saw arcing at the clamp.  Remember that the wire is electrically hot!

If you have a loose connection to a breaker, that could heat up the bus.

Copper or aluminum bus bars in the panel?  Aluminum oxide is non-conductive, a high-resistance connection can develop.

Feeder wires can be damaged in the ground, including long after the insulation is nicked.