Yeah I had this issue along with disconnecting at bosses for a few years. Basically you get some activity going, then there's a pause and you just stop receiving packets until your data pushes enough through. It seems like a bogus optimization in the modem/router for TCP.
It's not a client or server bug but something with your internet. Soda helped me do a ton of debugging with the server and the server wasn't at fault. Wireshark filtered for psobb showed that my connection just stopped receiving data until enough was pushed through, and then I'd see many duplicate ACKs and resends.