Air resistance? It’s mechanical. As soon as I stop pedaling at any speed. Is that normal?On higher speed, like on a Stromer, the air resistance increases significantly - if you stop pedaling, the air resistance helps breaking.
Try to increase the pressure of the tires; these large tires generate some rolling resistance.
Keep your fingers (for quick reaction time) on the brake lever - but if you pull only a little bit, you will activate the (scalable) motor brake - before the mechanical brake is aktive (like in a Tesla).