Sons 300m and I need help please!

We have a rule of thumb in the snowmobile world; a wet plug needs replacing. I realize that in the automobile world, this is overkill. And I realize that Platinum plugs ain't cheap, so perhaps a spark test might tell you something.
And, as mentioned,a compression test.
If your engine has both a crank sensor and a cam sensor,and no codes, then perhaps they've lost sync. However most ECUs only look to the cam sensor during cranking, and after that just count. It's hardly likely that a loss of cam sync would cause an engine to die,once running.But a dead spot on the TPS, hmmmmm
You don't, by any chance, have an aftermarket anti-theft device on it?