How long have you had the motorcycle & had it been running fine on your previous rides? I would make sure the battery is good & do a load test. I would also check the ignition coils to make sure they aren't getting hot. Also, make sure there isn't fuel starvation.
Ive had it 2 and a half years always ran well .all of a sudden this problem has poped up . I have new coils to go in and it had a new battery about 6 weeks ago ..just pray it starts with new coils on ..fingers crossed
the reason might be that your piston is seizing in the cylinder if it runs fine at low temperatures then check to see what temp it is. When it gets to be not running as good then check the temperature and compare to manufacture recommendations.
Hope I helped