Very mysterious dropping steps on one Y axis motor...I'm starting to lose it!!

[Hatchett Job]

Thanks so much for helping me with this.
Here's where I'm at.
Like you said I made a test toolpath that jogs the Y axis up and down 100 times.
First I ran it with motor A polarity reversed and sharing motor Ys signal from the control board. it worked fine.
Next I ran it with motor A slaved off motor Y with motor A step low activated and it lost steps.
Then I ran as above with motor Y step low activated and it lost slightly more steps.

[JAZZCNC]

Thanks so much for helping me with this.
Here's where I'm at.
Like you said I made a test toolpath that jogs the Y axis up and down 100 times.
First I ran it with motor A polarity reversed and sharing motor Ys signal from the control board. it worked fine.
Next I ran it with motor A slaved off motor Y with motor A step low activated and it lost steps.
Then I ran as above with motor Y step low activated and it lost slightly more steps.

What controller are you using and what frequency is it running at.? If the frequency is too fast then the drive opto's might not be able to keep up so steps are getting lost.