You can also try the following
1 - Delete and recreate the Auto provisioning policy. If it's too large and been working well till now, just delete the new rule, save, recreate
2 - Make sure that the policy is mapped to the controller and not the AP profile
3 - Delete the ap from the controller under Configuration >> Devices >> Device configuration >> Select AP >> Delete >> Commit and Save
4 - Reboot AP (you can always reset the AP for good measure)
Christoph S.