I've had this experience also any times, but also between 4th and 5th gear.
Even in a race in a fast corner a had this "false neutral" and believe me, I didn't like the bike at that time
I've learned to use more force for shifting gears, than you can feel that the movement of the gearlever has two phases. First a small movement and after that you feel the click of the gear-change.
(I hope my English is clear enough to understand)
I'm not sure what the reason is :???:
