Upto my knowledge i can suggest you the following point.
1.Use a 3 phase Choke at the incomer side to avoid the spike voltage.
2. Had you used proper Resistor for dynamic Braking as per the duty cycle?
3. Increase the resistance with 2% than the prescribed.
4. Use the exact wattage for the selection of Dynamic Braking Resistor.
5. Never design a circuit without an incomer semiconductor fuse for a drive application.
6. Does the servo motor
voltage matches the Controller voltage? If u use a lower rated controller will leads to the problem like the one you are facing.
7.If your incoming supply contains Harmonic then use proper filter to filter it, Since drive are sensitive to harmonics. [I not so confident about this point that will help you, but make a note of it.]
Since servo are sensitive application so check all the possible way to troubleshoot it out.
Kind Request :- People here in Rockwell India are not expert in drive application to give a quick solution. Make note about your problem to Rockwell USA.