I had the same experience initially. I've only used it on the race track, but try setting the shifter effort level in the settings menu... I set it to easiest/lightest (I think it is setting 1 of 3). I'm now not having an issue with up or down shifts.
I did notice at first that it took some getting used to. You need to give it a good crisp motion. I think initially I was rolling off the throttle a little, and also not being crisp with lever effort. I was seeing a bunch of false neutrals and missed up-shifts and it turned out that I wasn't using enough force.