I have a mix of R510, R610, and R710. All seem to have the connection failures. My Vsz is on version 6.3.1.0.227. I started having the connection failure problem on the first version of 3.6. My APs are on firmware version 3.6.1.0.354. I can downgrade the APs to the latest 3.5 version and the connection failures go away.
5ghz channel width is set to 80MHz.
On the non-DFS question. I have the channelization set to Auto. Out of 110 APs, i have 14 on channel 36 and 9 on channel 149