Modern Vespa

Idles and Runs perfectly fine, but when i come to a stop sign or a red light, and i try to accelerate suddenly the engine hesitates for a second. Total loss of power and it comes right back up. Any ideas?

Traction control kicking in because of low tire pressure is possible. Check tire pressure first, if still persists try asr calibration. Have you tried turning off asr?

I always turn off the traction control when I start the scooter, because of this hesitation and the same hesitation going over bumps. I would only leave it on if the roads were wet or gritty. Acceleration is much smoother without it.

The traction control compares the speed of the wheels. If the difference is too big it concludes there is a loss of traction on one of the wheels and it will reduce power.
It becomes more noticeable when the tire pressure is too low.
Inflate the tires. Without passenger front 1.8 bar (26 PSI) and rear 2.0 bar (29 PSI). If the ASR is still very noticeable you need to recalibrate the ASR. The procedure can be found in the manual, it will take a couple of minutes to perform.

i had the same issue on my gts ,i recalibrate the ASR and good to go

What they all said. My current tyres really need new valves but I hate the thought of having to have the back end dismantled. Soon maybe as I have to top them up weekly.