PS sends lots of small packets. Not a continuous stream, no long data transmissions. And they are sent insecurely. The keys are not speed and bandwidth, but timing and reliability. ISDN (64 kbps) can be superior to some cable connection even!
PS uses UDP: Packets are sent out, and the sender doesn't care if the receiver really receives the packet. If a packet gets lost ... well, sh** happens. This is different to TCP, used for HTTP and FTP transmissions - if a packet gets lost here, it gets requested again.
The strange thing is: If there is just some packet loss in delivering chat, you would not hear one sentence, but then again the next one. But you keep missing sentences ... so the reason must be slightly different. It seems to be related to the server believing that you are out of hearing range. Maybe the server missed a packet from you, telling it your last location. Because unsticking helps, it adds some evidence to this theory.