Currently working with D-Link support on an issue that I've narrowed down to having QOS active, and a user logging onto the GuestZone. When that scenario occurs, my regular connected clients get disconnected (both wired and wireless). If I don't use QOS, then no issues. Worked with D-Link for a while on it two weeks ago, and they sent me out another router. But unfortunately, the replacement DIR90L has the same issue. Just upgraded to the latest FW 1.07 and problem is still there. Supposed to get a call back from the next level up the support chain.
Since both routers have same issue... thinking the problem is somewhere in the firmware and wanted to see if anyone else is experiencing the same issues.
BTW - kudos to the thread on the workaround for Android issues (deactivating IPv6). Have been frustrated with the speed on my phone/Tablet until I came across that thread today.