Greyed out radio icon generaly indicates that the communication between AP <> Controller is having hard time. Based on my past experiences with many customers, it generally relates to congestion on the wired network which is limiting the ap<>controller communication.
It is best advised that APs are put in a seperate vlan for management purpose, putting APs and other common subnets (vlan) in same network exposes AP to unnecessary broadcast traffic which makes AP to process those unwanted broadcast traffic and causes overhead.
Also if you are tagging multiple VLANs on the switch port where APs connects to, avoid tagging unnecessary vlans such as vlan dedicated for wired network. Most of the wired broadcast traffic reaching the AP triggers problems that you have posted here. Once you have segregated vlans and limited the broadcast exposure on the switchport where APs are connected should help you to get rid of this issue.