Can you post a pic of of the spoiled work?
Mach will handle the small arcs and moves of the file. You didn't mention what you changed the tuning to. Since it works at 5x the scale,
lower your max velocity to something like 1/5 of the max and drop the velocity down accordingly. So the max velocity would be in the range of
6-10 IPM and accel is 1 or 2 and see what the tuning ramp looks like and if it won't skip ....and also drop you velocities in the program.
Since you making very small moves, your asking the stepper motors to accelerate almost instantaneously, and i donlt think your motors are capable of doing it.
So you can try lowering the vel and accel to allow enough time for the motors to react to what they need to do or you can provide motors with enough torque
at the desired velocity to accomplish the task. The lowered velocity on big files will increase the machining time.
RICH