I think it must also be understood that just because the controller indicates that an AP is offline, that it can still be PING'able. The loss of adoption just means that there's break in the communication link between an AP and the controller.
A more relevant test be to see if you can PING the AP from the controller....or the other way around. Or even better, can you MiNT PING in each direction?
Of those 9 APs that show offline, you say that they are in different RFDomains...not all 9 are in the same RFDomain, right?
If that's the case, what is common in the communication path between those 9 APs and the controller? Check those first. If the MiNT PING test fails, you'll need to locate at what point the MiNT traffic is being blocked/dropped.