Car shake when speed between 5kmh and 10 kmh

Today at a slow traffic, the car started to shake when the speed is slow. This is the fist time to happen.

The car is fairly new, 3 years old with new service done 2 weeks ago.

I suspect the gear box because the shake happens then the transmission goes from 2 to 1, with no brake applied.

Any ideas what is going on?

Update: the shake surprisingly gone in a second drive!!