The most common problem could be problems your Provider has. With more and more connections, stuff runs out of capacity. It's quite understandable with wires, where you can't pull more stuff than wires admit, like max of a water hose. It's less understood in wireless, where this guy "who was it" introduced the law that only a certain amount of data can be attainable at a certain time in a certain space - you can not have everyone wireless in a limited place, it will get stuck. Air will be filled, period.