From what you write, do I understand correctly that you see on the controller dashboard that the Access Point reaching out to the controller and doing an upgrade?
Is the controller properly licensed?
If so, have you whitelisted the AP?
Could it be that there is another controller running a different version of ArubaOS and the AP is jumping between those? That can result in an upgrade/downgrade loop.
Do you have access to the serial console, and if so, can you share the output of some reboot cycles of the AP (assuming it automatically reboots)?
In the case you don't want to share the logs, or don't have access to the console, this discovery, upgrade and whitelist process is extensively covered in Aruba training. So if you have access to an Aruba partner, or Aruba Support, interactively troubleshooting is probably much faster than discussing it here with limited information.