Do you remember the time period of using the set up wizard and when you tested QoS?
Did you set up any IP reservations before testing QoS?
I'm noticing if I set up IP reservations and don't configure QoS right after setup wizard completes, if I configure it a bit later on, it won't work right. If I configure QoS right after using the setup wizard, QoS works...I'm trying to narrow down what might be causing QoS to stop working. I tested this by skipping the setup wizard after a factory reset and just loaded my saved config file. QoS didn't work right. I did another factory reset and this time used the setup wizard and configured QoS and it worked. I reset once more, used setup wizard, started reserving IP addresses, 5-10 minutes doing this, then tried QoS and again, QoS didn't work right. When it works, I see the 80sec reboot window and the router reboots. So last thing I did was a factory reset, used the setup wizard, immediately set up QoS, Up and Down link speeds, saw the reboot window, then after the reboot I set up a couple of reservations only. I was still able to set my xbox 360 into the high priority section and save it and saw the 80sec reboot window.
Let me know if you can try any of this. Especially doing a reset, setup wizard and immediately set up QoS...
I've pasted this along to D-link for review.