Speed-related problems in X3 are generally caused by the induction head of the speed sensor being too far away from the Hall element to detect changes. You need to turn the speed sensor head to the right a little bit to detect changes. If not, then you need to replace the motherboard. If you need to replace the motherboard, please contact service2@thinkrider.com  and we will provide you with a new motherboard. You can learn how to do it in the video below.
X3 bending speed sensor video: https://youtu.be/yvl64Fa9lSw