AFAIK minebea doesnt sell to end users like us. They make custom stepper motors for other companies. Therefore end user support is not their "thing". Which probably explains the behavior. That stepper is probably recuperated from some discarded printer or similar. To test the stepper, use a multimeter to measure coil resistance and to ensure they arent interupted or shorted in a wrong way.
Also afaik, you may need a few R and C near the 555.
Also afaik, you may need a few R and C near the 555.