Plugs look good, maybe a tiny bit lean, the jetting would be marginal if the weather turned colder. You have tried all the stuff I would have tried, except for unscrewing the plug cap and snipping 1/4" of wire off the wire, then screwing the cap back in. Sometimes the connection at the wire to the plug gets bad, and fresh wire may help.
If the compression gauge is accurate, 100 is marginal for a good running engine. It may be time for some new rings/pistons. But I would be going like you have; searching for an electrical issue that is worse when the engine is warm.
Good luck.. hunting down these kind of gremlins can be an exercise in frustration!!
2007 RMK 700, 2008 RMK 600, 1995 AC Prowler 2-up, 1980? AC Cheetah