Hello people - an unusual issue using a 2 axis EleksMaker Motherboard

Something to get the Electronic Wizards out there thinking.

the Basic problem
I am cutting a SQUARE from a piece of ply with a high powered dual diode laser module & its dedicated controller.
My laser puts out about 30% LESS power when moving front-to-rear in the Y axis direction
Y drives 2 motors... so logically I thought was that the laser is being starved of power...
Nope... wrong again...

Part way thru the Y movement I pulled a Y motor connection & the laser instantly puts out the same/proper power as when moving in the X direction - left to right...
so, I fitted a 10 amp 12 volt power supply for the motherboard & laser, and hooked up an external stepper amplifier solely to drive the two Y motors - with its own 12volt 10amp power supply.
This external stepper amplifier is capable of driving BIG Nema23 motors or bigger, and has no problem driving a pair of Nema17 motors.

The same issue occurs, that the laser is weaker in Y direction...
So again I pull a single Y motor connector & the laser instantly pushed more power & makes the cut.

The motherboard & laser have one 10 amp power supply
AND
the Y motors have ANOTHER 10 amp power supply via the stepper amplifier,
yet the laser still drops power in Y direction unless one Y motor is unplugged mid run...at which point the laser resumes a clean cut again.

The two powers supply units work, and the only electrical connection between the stepper amplifier and the motherboard are the signal feeds to control the external Y motors amplifier.

I have swapped out the Y motors for smaller lower powered units, swapped out the motor cables, swapped out the mother board & multiple nano-boards.

It seams like there is some electrical interference (RF or Capacitance) that is feeding back from the dual Y motors that is interfering with the laser signal....
So,
I fitted ferrite rings to the motor cables - to all 3 motors, and to the power supplies, and the laser signal cable from the Motherboard to the Laser control module...

and still the laser reduces power in the Y direction.
Has any one got any ideas on this & what could solve the problem.