I have sensored motors that for no reason have started cogging or I buy used and may have been cogging and I just never hooked them till now. What can be done to stop or fix motor cogging, all suggestions welcome.

Try the following, in order:

1.) Reduce the motor timing
2.) Replace the sensor cable
3.) Remove the sensor board from the motor, clean it, inspect it for visible damage, and reinstall it.
4.) Replace the sensor board

Thanks, I will go through them step by step in hopes to fix them.