I am assuming you have it in RAP mode.
What is the network between the AP and the controller?
You should obtain the tech support from the AP when it connects so you can get an idea what could be going on.
You can also get the output of:
"show ap debug counters ap-name <name of ap>" to see if it is rebootstrapping.
Disconnecting and getting a different inner ip suggests that there is a network issue between the RAP and the controller. You should try to eliminate that by connecting the AP as a RAP to the controller on your local LAN and see if it has the same issue.