Motorcycles only start at very high speed, what do they do?

Hey guys, I’ve been driving a brand new Z125 (2018) for almost 2000km now and I haven’t had any problems until now. Now I went home from school today, stopped on a dirt road to take a nice picture of my little one quickly and when I wanted to leave again, I noticed that something was wrong. I first thought I was in neutral gear, because she just didn’t want to go off, but this was not the case. Only in the high speed range she moved sic h tormentingly slowly forward, but was then also directly in the limiter and when I switched up it accelerated also only from about 7k turns (I was worth under these, it became slower even with constant gas). I was not far away from home, so for safety reason I pushed my machine home, on the one hand, because I did not want to destroy even more, on the other hand, because otherwise she would believe my whole neighborhood would have screamed together. ch already thought about what I could have done so wrong, does that help to identify the error: – not always warm up (that’s right) – yesterday my buddy drove with her and strangled her several times (softer 5x) and turned pretty high at the beginning – last Saturday I tried burnouts once (so 2-3 pieces) – completely. too high speed and thus damage of the gear? I hope you can help me