I have never seen a stepper fail in that way. So either loose pulleys, or incorrect/uneven belt tension, bearings tension set to high on the rails, weak steppers, something rubbing.
A video of it happening, maybe a showing the rollers not moving smoothly. Your spec sheet for your steppers, and what voltage you set your drivers to, what software are you using to generate your gcode, or upload your gcode, step rate? Do all axis move the correct distance to at last .1mm? I have asked some of these questions before.
You just keep giving bits of info and rejecting my possible solutions. Give as much detail as you can.
Have you tried my test gcode, Does it work smoothly? Tried my torture test, does your machine handle it without skipping steps?