Supervisor:

The use of a 555 is not solid. The 555 is not specified to work as specified before power reaches full value. Use a real supervisor.

Noise:

Start stop of a motor is a real bitch, I have had many problems with same. Some questions:
How long is the interconnect from the uC to the motor ?
Is the uC powered from a separate power line ?
How do you power the side of the optocouplers that face the motor ?

Erik