3040T and Y axis shift

Hi 
Some time ago I've upgraded my 3040. I've replaced all electronics and now I'm using hy-jk02-m bob + 4xTB6600. Stepper motors are still original Anchuan 57hd0401 1.8deg 2A.I've also upgraded spindle to 2.2kw driven by hy inverter. Only one Power supply for motors is 24v 20A. Currently I've got an issue with Y axis. I've tried to cut different size of squares in plywood. Everything went OK, after measuring difference was that small so I can take it as a measure error. In one of the tests I've cut 30x30 square and then I've tried to cut it diagonally. Unfortunately I've noticed shift during cutting in X+Y - direction. Because of that axis is shifted. I'm not sure what's is wrong. Mechanically I cannot see any issue with coupler or driving nut. I made a video from this test. Please have a look here :





Efect in attachment 
 

At the beginning all of them were set to 2A current to match steppers. Then I set Y axis driver to 2.5A and that's what you can see on the video.Regarding microstepping I've set it up to 8. 

We can close this one...
I ended replacing stepper on Y axis
Now I've got nema23 3nm closed loop, and no more issues. No maybe just one, not enough space in my cabinet. I will need to buy something bigger, cause in future I will replace stepper on x axis + separate power supply.