Odog. Did you have any more video of the saw running, that shows as you switched the saw off?
we'd want to see the trigger and switch area while it's done.
helps to see what might be moved or shifted.
You just never know what someone on here might notice!
I'm in the camp with "the hot spot in the saw" theory, But....
Are you working in an area that would be OK to run the saw after dark?
No neighbors to bother, noise rules, etc.
I'm just curious to see if and where any sparking is visible.
There was an interesting case with push mower brought in to the shop where I worked.
It would run with the plug wire off (but with the boot just touching the spark plug tip).
But then if you put the wire on, properly, it wouldn't crank.
Turned out to be a "dry" soot fouled plug (four cycle engine).
hmm... What was happening was the extra gap (ONLY about 3/4") was working as a "booster gap" and would let the spark jump the plug gap.
But when the boot was properly placed on the plug top, the spark was bled off through the carbon deposits.
I found it Interesting how that gap gives an Inertial effect to the electricity!
But I, seriously, do not expect that we have a booster gap situation with your saw though.
Sorry that I couldn't find a better explanation link about a booster gap. This is just about spark plugs with it built in.
http://firetrucksandequipment.tpub.com/TM-5-4210-230-14P-1/css/TM-5-4210-230-14P-1_615.h
And here is a link with some explanations of heat range and how heat travels through the spark plug.
It also tells what the different heat range numbers have to do with your engine.
( hint.... Self cleaning/less fouling of the spark plug is the main thing )
http://www.briskusa.com/spark_plug_cross_reference_heat_range_chart