spray wd40 in the chamber and put the plug back in , if the ignition timings off a little it will still fire,,
your coil lead to spark plug my go faulty when its in position but correct itself when testing the plug/spark outside the engine(the bend my correct a breakage)
do you have the use of a "colour tune kit"
do you have the use of timing strobe light
have you used a compression tester
your certain your valves are closed at tdc
you have checked the obvious
side stand switch
neutral switch
handlebar on/off switch
ignition switch
dont be cross

,, it sounds like your sure you have tested everything and everything is fine,,but its not starting so you have misunderstood something,,breaking it down, fuel/compression/spark,bang= power,then theres the failsafe devices to consider,