If the shoulder is getting dislocated post surgery, there is a possibility of another tear around the ligaments of shoulder..
Next Steps
You should get a fresh MRI of shoulder to know the current status of lesions in shoulder joint.. There is a possibility that you may require another surgery for correction of the associated cause.
Health Tips
You need to take precautions and avoid any movements which may cause stress over the shoulder and may cause dislocation again.. If you are involved in sports activities, better to avoid it for now..