How well adjusted to your foot and riding position is your shift lever, usually having to lift your foot too far to shift will "short" shift and occasionally not select properly .
Often happens when riding aggressively as you tend to sit further forward ,putting your foot away from the lever even more
And the busa 5-6 shift is not as quick as the other gears as its operating both shift forks in the gearbox, pulling one gear out shifting forks then putting the other gear in, most of the other shifts use only one fork shuttling from eg: one gearset on the left of the fork to the other on the right
so be more definite and allow for a longer shift time
Often happens when riding aggressively as you tend to sit further forward ,putting your foot away from the lever even more
And the busa 5-6 shift is not as quick as the other gears as its operating both shift forks in the gearbox, pulling one gear out shifting forks then putting the other gear in, most of the other shifts use only one fork shuttling from eg: one gearset on the left of the fork to the other on the right
so be more definite and allow for a longer shift time