I have new R550 APs. So I'm trying to connect them to my vSmart Zone. So I have to update the controller to version 184.108.40.206.515 (AP Firmware 220.127.116.11.1017).
My other APs (R500, R510, R710, T310) were able to connect to the controller and download the firmware. But the R550 went online and showed "New Configuration". Then he went offline and back online and offline again. Multiple times. Then he stayed offline.
I have tried several times to reflash it into the standalone firmware and reconnect to the controller. Same behavior. Again and again.
You stated that other APs had no issues connecting and upgrading. Are they on exactly same VLAN as R550? Different firewall rules for different VLANs may be reason for fault. Also upgrading already adopted AP and adopting standalone AP isn't exactly same process, it may require proper vSZ configuration to happen. What are messages in AP event log? You can get log from AP itself, it can show more about what is wrong with it.
After you try to adopt AP, what in the end is AP status -- does it stay on same standalone image or is upgraded to vSZ image? Make factory reset and try again connect it to vSZ without reloading image.
Otherwise it looks absolutely weird. I can confirm that I was able to connect R550 APs to same vSZ version without any issues. I recommend you open support case with Ruckus -- it may be AP hardware problem, or some software bug.