Hi everyone, I hope this is the right section of the forum.
I have an issue with my cnc, it's a 3-axis (dual y driver/motor) closed-loop, which I won't name for correctness.
The machine is controlled by Mach3 with a legitimate license and an XHC 4 Ethernet board (already replaced with no luck).
Every now and then, in a completely random manner, during operation, the second Y-axis (A) of the machine stops while the first one continues to move, twisting the gantry until it can't move anymore, and then it goes into an error state.
After this problem occurs, resetting the drivers with an e-stop or even turning off the machine allows me to move it regularly with jog controls. However, if I give a G-code command, axis A remains still, and of course, axis Y goes into error after a short movement and this give me the opportunity to make some test (I've already done countless tests with wiring, drivers, and motors swapping etc). This time I tried connecting an oscilloscope to the outputs of the control board, and it confirms that there's no signal coming from the A-axis port. More precisely there's signal when jogging but there's no signal when sending gcode commands.
You can find a video at this link: https://youtu.be/OxL9pzbboVc
Oscilloscope probes are connected to Y and A axis

Among the tests performed with no success:

Replaced the control board
Used 2 different PCs
Tested 3 different operating systems (Windows XP, 7, 10)
Tried 3 versions of Mach (3.43.66, .60, .22)
Tested 3 versions of XHC board drivers (3.15, 3.17, 3.19)

Does anyone have any idea on Wath can it be the problem?
Thank you in advance.

Long story short:
The control board, without drivers connected, on the A axis (slave to Y) as output signal when jogging but no output signal when I send gcode command.
Control board already replaced.
Tried differ is, different mach3 versions and different control board plugin releases