I have a 19 and have had something similar happen and took me by surprise. Hasn't happened often but the last time stood out as loud. I thought it had to do with my technique being off, but I truly wasn't paying attention to how that came about.

I'm going to see if thjs happens again and more frequently and whether I was properly using the clutch or not.

 

I've had this happen once or twice. Sort of. Go to shift between any of the other gear combinations besides first to second, and the thing falls into a false neutral. Could be the shift detent spring being weak. That's a bit of a problem on our bikes, I'm to understand. I just installed the Factory Pro shift spring on mine this morning. Haven't ridden it yet but just shifting it on a paddock stand feels really good and positive. Not weak and whimpy like before.

 

Happens to me very rarely and is if I'm just a bit light on the shift, without preloading the lever and/or a bit low in RPM. (IMO). Nothing wrong with the bike in my case - if I get into it, high rpm, positive changes then doesn't happen.

 

I think this is similar to me, sometimes I think I don’t push the gear lever arm high enough, I wonder if there is a way to adjusting this lever arm to make it easier to upshift..