Start simple; how is your oil level?
Check with the bike upright (on centerstand is OK), and don't screw the dipstick back in after you first wipe it off - just set it on top of the threaded hole and pull it out again to read the level.
It doesn't sound like you have a problem since it's only occurred twice. Apparently, you're catching a false neutral upshifting 3rd to 4th, which is an incompleted shift where the sliding clutch gets caught between the two gears. On the GStwin, it's more common to catch a false neutral between 5th and 6th. Good timing and a firm upshift under acceleration will minimize the occurrence
The oil level was the first thing i checked. No oil is used yet. I will try to shift more firm, but i was not aware of that a engine could go i false neutral :dunno:
/tralala