You posted this in the wireless forum so I assume you are using wireless.
To be rather blunt but why would you not expect it to run that way sometime. Every place you look you see people say do not play online games on wireless. What you are seeing is exactly why it is not recommended to run wireless. It may work one minute and not the next. There are many things that affect wireless performance many of which are completely out of your control...the most common being a neighbor got a new wireless router.