Strange, I had the exact same experience yesterday with my Vitpilen 401 (late 2018 and 4300 Km).
Monday on my way to work, I rode about 500 meters and it just died after the traffic light was green, after I switched to second gear. I tried to start it again, no luck, third try it run for 5-10 seconds and died again. Walked home on the bike lanes (The Netherlands) and just 500 meters from home.
I had a good ride on Friday night and filled it full with gas and parked it in the garden. Oil level was good. Last Oil fill was with 1000 Km.
Tonight, I first want to make sure the oil level is ok again and try to ride it again. Because Oil level was suddenly around minimum when I checked it on Monday evening.