Have you ever found yourself between gears, in a neutral somewhere other than the real deal between first and second? A false neutral is a neutral that occurs between gears other than first and second, where true neutral resides. False neutrals usually happen when shifting the transmission up from fourth to fifth or from fifth to sixth, and they are distracting and dangerous since you won’t have drive or engine braking as expected.
First let's talk about why they happen. A false neutral is essentially an incomplete shift. You've moved the shift lever enough that the dogs on the last set of gears were successfully disengaged, but didn't move things along far enough to mesh the next set of gear dogs. The drum, shift forks, and gears are literally between positions, and that's possible because there needs to be a little lateral clearance between gears so that it's impossible to have two gears engaged at once. The flipside is that you can have no gears engaged, which, I think we can all agree, is better than having your transmission explode.
When you get a false neutral, your best bet is to pull in the clutch and re-shift. Unfortunately the transmission may make an unpleasant noise when it finally goes into gear, but you can reduce or eliminate it by blipping the throttle to match engine revs to your ground speed.
The best option, though, is to avoid false neutrals altogether, and the best way to do that is to simply be deliberate with your footwork and push the shift lever all the way through it’s travel. Yep, it’s that simple. If however you’re still having issues with the bike hitting false neutrals or jumping out of gear, you should check the adjustment on your shift linkage. You could also have damaged gear dogs, a bent shift fork, or maybe the shift star is loose on the shift drum.
Another question that cropped up a lot in the comments section of the transmission video had to do with the clunk you hear and feel as you shift into first gear from neutral at a standstill. That's perfectly normal, and it's just what happens when the gear dogs on a spinning cog engage with a stationary gear or a gear that's rotating at a drastically different speed. I know what you're thinking—if the clutch is pulled in, why is the input shaft spinning? In a perfect, friction-free world it wouldn't be, but fluid drag between the clutch plates causes the transmission shafts to spin.