All

The fact it wouldnt kick over says hydo lock, but that wouldnt happen after an unwanted shutdown. then by turning the rear wheel (in gear?) freeing it up points to kick start mechanism? Dont think stuck valve or skipping a tooth cuz those dont fix themselves and crank/piston should still move. Blocked exhaust wouldnt cause a stuck kicker either. Maybe piston seized, then when it cooled down it came unstuck? Interesting set of symptoms for sure. Is there oil in the engine?

I say something got stuck and by turning the rear wheel in gear you unstuck it. Probably more then one issue. Something loose or out of place somewhere. Take top end apart and check everything. I think you will find the answer. Make sure exhaust is clear too. Its only a blockage in the exhaust circuit that will cause it to build pressure, or it was the kickstart mechanism making you think it was “building pressure”

I would check your cam chain, tensioner and guides like Homer suggested. Maybe your bike jumped out of timing, my buddy’s 2012 KX450 did that. Good luck

Only thing i come up with is a sticky exhaust valve. Of course it could be malfuntion of kick start mechanism. Did it just quit riding or did you stall/crash the bike.

Your kickstarter getting tighter and tighter as you kick makes em think you are getting hydro-locked or vapor-locked but the description of how it happens isn't consistent with that. My Homer-brain is telling me that I'd be looking closely at your cam chain tensioner? I dunno...weird stuff.

That sounds weird. I have a 17 and had problems once after some moisture got into the electronics, I disconnected and cleaned them all and it has been fine since. My symptoms were totally different. Maybe a problem with the fuel cap or vent, if none of the suggestions above make a difference.

Has the fuel tank been removed recently? Make sure the fuel line is not pinched or twisted. Sounds silly, but it’s very easy to do.

Check your fuel filter.