Good to know there are a few ak 550 owners out there. I don't think this bike was introduced in the US until 2021 (could be wrong), anyway I bought an ak550 3 weeks ago from a dealer in Phoenix, az. It was the company's demo and had 438 miles on lit. I was always reluctant to buy a demo "cuz it could have been ridden hard in the 1st couple of hundred miles. This one though was in perfect condition with absolutely no problems. I'm very happy since I have had many scooters in my life but not one with the power of a motorcycle.
To address the problem you brought up. I find that I get intermittent vibration (thru the foot board) when I not putting the engine under load such as when I'm going 56-60 on level ground while backing off the throttle a bit and not losing speed. Otherwise I don't get the feeling. I have a Piaggio BV 500 also and find that that happens to it as well but not as noticeable. I suspect this will go away with more bread-in time.
WEL, thanks for starting a conversation.