What you are experiencing is actually electronic slip. The bike is limited to a maximum amount of force you can exert on the pedals. In order to save your electronics and your motor, we allow for “slip” if you exceed the maximum force. That maximum force goes up with your cadence. So below 30 rpm you can feel slip. Above 30 rpm almost no-one can push hard enough to reach the limit (but we have seen some professional TRACK SPRINTERS reach it). Since this is only a problem for starting, you will not experience this slip during your workouts.