There are no guarantees with the internet.  When the pipe anywhere along the route overflows the packets are dropped. Good ISP’s have an excess of bandwidth to avoid most of the issues but smaller ones may not be able to afford the extra bandwidth.  QoS must be enabled over the entire path to be able to use that feature of the internet. It also comes at a cost much like a static IP.  Voice data is the hardest hit when packets are dropped as good voice recreation requires all the packets to be in sequence in a timely fashion to get good audio.