I've just received a SEB-350D and can add a few things you can check.
Firstly check all the nuts, bolts and screws on the frame and wheels. Pay specific attention to the nuts on the wheels.
I noticed that the rear wheel (installed at the factory) had been tightened so tight it actually deformed the washers. I thought this was a bit over the top and tightened the front wheel tight but not that tight (I'm famous for stripping nuts).
A few days later I noticed it was loose so you really need to ensure its tight.
Also check your spokes, again I didn't do this and broke 2 of them in the first 3 or 4 rides (both went on the same ride).
I've since checked and tightened where necessary (another broke just today unfortunately).
Make sure your Lights and Horn if you have them are tightened up nice and firm.
The only other issue I have had is when caught in the rain I get a shock from the thumb wheel and the hub motors stop driving. I don't think its water getting into the harness or motors but might be moisture getting into the thumb throttle or the connection that hosts the cables for the throttle, brakes, lights etc. I'm toying with the idea of opening up the throttle and sealing it with silicone.
Hope this helps. Apart from the above the bike has been good, it has great acceleration, LIFEPO4 Battery life is good the frames a little heavy but I can live with it. Hope you enjoy yours as much as I enjoy mine.