Hi haare - this is very normal and not an error.
Just found the lift from 2015 and quite low AR.
Which means, at low speeds it will make a soft stall, giving you a warning as a vibration, which is really cool, as then you know you are on the verge to stalling, but havent stalled yet.
It is how low AR wings works, and great
Higher AR wings (more span and less average chord) works just the opposite, they work well to a certain point, but then they stall without any warning....
Hope this explains - dont worry, your wing is spot on and works just as desired - be happy you got this warning you are on the verge of riding too slow