This cannot happen -- ever, at least on GS 150 or CG 125. (A)
The gears come down one by one and not instantaneously if you are in a higher gear.
Specially on GS 150, you have to do a clutch release between each interval otherwise the gear won't downshift.
And first one is hard to get back until you pretty much idle the speed.
This is because there is some sort of lock!
It is possible some transmission sprocket might have slipped in your case and screwed up rest of the sh*t with engine.
This is all because Ravi doesn't have years of expertise like other competitors.
Now I am beginning to think if all Piaggio bikes are vulnerable to this insanely crazy glitch in transmission :mad: