is it possible that the original configuration setting ist not correct? The laser uses two stepper motors for the Y-Axis. So there are some connections that will copy the steps from driver 2 to 3. Therefore the pin assignment changed for the Z-Axis as this will now use the 4th driver.
What one cannot change is the wiring/assignment of the current limit.
In my opinion this leads to the following config setting:
alpha_current 1.9 # X stepper motor current - no change beta_current 1.9 # Y stepper motor current - no change gamma_current 1.9 # Second Y stepper motor current - CHANGED delta_current 1.5 # Z stepper motor current - CHANGED
If you are using a 4th axis then this goes to epsilon
epsilon_current 1.5 # A stepper motor current
Am I right?