Cisco offers an option to put newly joined APs into a special AP-group. This group called „Out-Of-Box“ sets per default the radios administratively down and does not include any WLANs. The thoughts behind this are, that brand new APs can join the controller, but do not affect the existing RF infrastructure.
Under normal condition the radios will be enabled as soon as you move the AP to another group. Unfortunately with several code versions (e.g. 8.5.151) the radios remain down after switch from Out-Of-Box to another group.
Although Cisco does not list an official bug yet, there are several posts out there complaining about this issue.
There’s a simple workaround. You just have to change the RF-Profile in the AP-group from „Out-Of-Box-11A/B“ to „none“ (or any other RF-profile).
To make sure that this does not have an impact on the RF, I did a packet capture. Despite the radios are up, the AP does not send any beacons. So this workaround works perfectly fine.