Its because you've done an Xbox live test after it not connecting and its given you the first problem solving suggesting, which is the MTU idea. I did it a few hours ago to see what the status said and it did the same mate. If you press "tried this" or whatever it gives you another idea to try.

From memory my message said 7:01am (midnight for the yanks) until the same this morning, up to 24 hours. Sometimes a dashboard update or maintenance can cause a few niggles for a bit after though.