The engine is running fine for 20 minutes so what could possibly alter in that time?. Something heat related. Do you think it's worth checking the plug lead? the cap has been changed. When cold it's fine but a hot wire especially if its core is made of carbon can become brittle when hot and cause an intermittent spark. Failing that the valves may not be seating properly hence the low compression. Has ron had the cap of the cut of switch and examined the contacts/wires properly?.Plug looks better to me. The NGK chart (I'm guessing) would be for 4 stroke engines ie no oil in the mix. Anyway don't think it's weak now.
The apparent obsession with the temp was because I could think of nothing that would permanently damage a new plug (internal arcing) except heat.
If it was heat damage, and the gauge wasn't showing high temp, the gauge / thermistor had to be faulty. Thermistor is also next to plug and may be cooked.
That may seem irrelevant, but the only temp indication we have is the gauge, and we needed to know for sure if the engine was overheating, or not.
Hope that makes sense, I know what I mean, but may not be passing it across too well.
Even then a bit puzzled. the cylinder jacket is watercooled, but is the cylinder head ? No fins and long spark plug thread suggests it may be, but not sure.
Will see what pictures I can find, manual I have is not clear in that area.
The compression reading is low for a high compression ratio engine, but don't think just wear alone would cause overheating,
could be loss of compression due to expansion, but it would need to be pretty drastic to stop a running engine.
If there's ring /bore damage as well, that's another matter
@ Ron, This is just discussion, suggest you ignore above for now. More important to try bike and see what changes, if any.