Biggest issue currently is that APs will (seemingly) randomly stop authenticating clients (just normal WPA2 PSK clients). In the ZD you will then see clients on that AP being "blocked for too many failed attempts" and the clients start re-prompting for valid credentials. Restarting the affected AP immediately fixes the issue. Because of the randomness (both in time between occurrences and in which AP is affected) my theory is that some "bad" device is entering the network and the AP doesn't handle it well. In any case, it's extremely frustrating to have to routinely reboot APs to keep them working. I miss the glory days of 7962s that were exceedingly stable. And don't even get me started on the practice of Ruckus releasing new APs with features missing (airtime fairness on 5g, wlan prioritization, etc). Grrrr.
I thought they had solved most of the client connectivity issues in 9.8 MR3, for the r700 at least anyway.
The only one they have not fixed that I am aware of is when you have force DHCP enabled and the clients cannot roam (I found this one myself and am eagerly awaiting a fix)
ATF for the 5GHz is going to take some time for 802.11ac, as most other vendors have opted to use 3 radio AP's (the 3rd radio being 802.11ac clients only)