'83 GPz 550 Warm Start Issue

I have a stock '83 GPz550. It starts no problem when cold, every time. Occasionally, after riding a while, then stopping, then going to ride again, it won't start.
When that happens, everything else is normal - turning the ignition switch turns on the lights, activates the gauges, etc. - except depressing the start button does nothing. The engine doesn't crank, the starter solenoid doesn't spin, no noise/sounds whatsoever.
I've read some posts here related to starter lockout and other potential starting issues.
But the weird thing in my case is that it only happens when the bike is warmed up, then shut off, then tried to start warm. And, it does it only about 30-40% of the time.
Eventually, after turning the key, sliding the start button, jiggling the starter lockout wires, it will start. But the issue doesn't seem connected to any of things in particular.
Just wondering if anybody can help diagnose this - especially the connection to the issue occurring only when the bike is warmed up, and then only sporadically.
Thanks!

To rule out the battery and starter itself, you can just jump the starter solenoid with a big piece of metal. THe arc might take out a chunk so use a scrap piece or disposable tool.

Jump across the two big bolts on the starter solenoid.

If it cranks that way, then the battery and motor are good, obviously. So then you will have to start hunting down a wiring or switch issue.