Odd issue with X and Y. New build

Black ground wire should be last on all stepper motors. On mine i had to switch the Green and Red on Y2 axis only they were working against each other. when you mirror motors need to mirror wiring. I hope this helps

There may be. But you need to figure out what works with your machine.

I listened and watched your video. The appears to be slipping but the belt is not slipping the problem is in the IPM rate. The axis is going up too fast and going down too fast and you are losing steps. Slow the thing down and that will solve your problem.