Faulty x axis

so some backround:
finished my cnc with my own printeed parts and everything else came from the store on this website. i have the wiring harness and the main kit, my only other part is a dewalt 660. My problem is as follows: during longer stretchs of time for my y axis, it is very faulty, working on and off not really wanting to choose when it works for a long time. I no for sure that it is not a tightening problem, but there is nothing else I can think of. I am very dry on knowledge for how to start fixing this problem. just to clarify, it is one motor, not both on the axis, resulting in the other one moving fine then getting stuck. Any more info can be provided, but I didn’t know if anything else would help.
thanks in advance.

Double check the connections and best practice is to tape them so they don’t wiggle.