Client and server can both get stuck waiting for packet sequence history flush

The issue occurs when both instances have a significant difference between their last sent and last ack'd sequence number, as they will begin waiting for the sequence history to be flushed for a packet. While they wait for this ack, they will reject incoming packets, causing them to stop sending acks for received packets. With both instances doing this, neither will receive an ack for the sequence number they're waiting on.

Issue seems to occur rarely under poor networking conditions, particularly when bandwidth is being throttled. With significant latency, packet loss, and bandwidth limiting, a client and server sending a high amount of traffic between each other can end up in this state.