Please excuse my English as I live in Spain and English is not my mother language.
I had the same problems that most of you:
The AP stopped working properly once a day or two. Clients could connect to the AP, but the AP didn't connect to the wired network.
Another problem is that some clients didn't connect to the AP any more until a restart of the AP.
I had also periodic problems with dhcp.
As there are no new firmwares yet and most of you had made all sorts of setup combinations, there was a new one I think nobody had tried.
I use 3 of the 4 ssids this AP can manage, but there was only one thing I had not tried. The "Group Key Update Interval" was set the same in all ssids. I have changed them all (default was 1800), to 2400, 3000, 4200, 5400. I added the fourth ssid only to set its "Group Key Update Interval", then I deleted the ssid.
Now I have been 2 weeks without a single need to restart (switch off and on) the ap.
It manages a wifi printer, 2 android phones, a wii, 2 laptops, a tablet, an ip camera... and some laptops of some neighbours. There has been NO problems at all. The worst problem was the printer. It lost the connection every day, so I had to switch ap on an off. That problem has disappeared.
It seems that having the same "Group Key Update Interval" makes the ap to try to update it exactly at the some time, and it caused a leak of resources. I don't know the reason, but this was my last try before to get rid of it, tired of waiting for a solution from dlink.
Now my ap, 2 years after, does what it was supposed to do.
Regards.