Not sure if this is related to the 5GHz issue, but in our household, nearly all of us were experiencing regular disconnection issues on 2.4GHz b/g/n. (b/g protection mode was on, Xbox mode was on)
When this issue would occur, nearly all our devices (about 11 of them on different platforms) would get disconnected and would try to reconnect but fail. Manually trying to reconnect would result in a failure as well. We are using channel 11, which isn't used by neighboring APs and is the least polluted channel.
The temporary fix for that issue was to reboot the router. However, I found that turning off b and g and running exclusively on n solved the issue permanently. This solution is acceptable for us since all our devices are n capable, but just thought I'd report it anyways.
Edit: Forgot to mention, I'm on an AC66U - brand new router, loaded with Merlin's beta firmware as soon as I purchased it.
Edit2: Issue has re-surfaced. Changing to n didn't really solve anything. Rebooting solves the issue but only temporarily.