When would a chronic ankle pain after an ankle surgery be a cause of worry or an indication that there is a problem with the surgery?

This is quite a challening question to answer without further information. You see, it depends on

1. What was the mechanism of injury?
2. What was the injury?
3. What was the operation?
4. Does the patient have any other concurrent medical issues?
5. Did the patient attend follow-up or rehabilitation?

If you are having chronic pain following your operation, it would be best to consult your treating clinician in the first instance, or if this is not possilbe, obtain a polyclinic referral to your local hospital for a reassessment.

I hope this helps.