Your eight steps mentioned is the different phases used by the motor, i.e. different combinations of current on/off/reversed to the different coils.

If you can't run the motor 100 steps forward then 100 steps backwards and repeat this again and again and always end up at the same position, then you either have an issue with the drive currents, or with how the phases are driven or with the speed you use when running the motor. Maybe you accelerate too fast or it's the gradual slow-down that fails.

Does the equipment have any calibration sensor so you can slow-step the moving part until you reach the sensor and then perform different movements before you try to return to the index sensor location again? In that case, you should see what happens if you slow down everything until you find maximum acceleration and maximum speed that makes the gear stop missing steps.

Another thing to consider is that a stepper motor requires that the coils are driven to be semi-locked at the current step. If the drive current is turned off, then the motor will rotate with little resistance. So just turning off all drive when the motor is running will result in the moving part to continue to move for a while. And vibrations or other forces on the moving part can have it change location without you knowing that the motor ticks steps.

So after you have calibrated your position using an index switch, you need to keep the motor driven at all times just to make sure it has enough break torque.

Unless you have designed the hardware, I would expect the hardware to have some specification about what the highest step speed is you may start with. And then how fast you can increase the step speed. And the fastest step speed you can maintain. But these figures are totally depending on mass of the moving part, how much movement each motor step represents, the torque of the motor and how much current you drive it with. If all timing parameters aren't well documented, you will have to figure them out yourself.

Have you tried to just run the motor at a really low speed to make sure it doesn't miss steps?