My 1992 bike had this issue a few years ago. The cause was dirty/blackened contacts in the starter button. I checked and cleaned them again recently even though they looked clean, so I rule that out as the cause this time.
Situation: with side stand up, trans in neutral with light on, press button - nothing, no click, nothing. If I pull the clutch lever in it will start. Sometimes if I keep stabbing the starter button without the clutch lever in it will eventually start. Side stand up or down seems to make it no better or worse - just the clutch lever. As I said in the heading, it's an intermittent issue.
What's the cause and cure?