The only oddity I have noticed with Github is that if a network stack is optimized for high throughput large initial window size they seem to choke on it but yo

The only oddity I have noticed with Github is that if a network stack is optimized for high throughput large initial window size they seem to choke on it but you would know if you tuned for that on your router or each of your machines so it's probably not that. Have you by chance closed your browser, started tcpdump then fed the cap file into Wireshark and run the Analyze -> Expert Information tool? What OS are you using? If Linux, as root: tcpdump -i any -p -NNnn -s0 -v -c10000 -w /dev/shm/p443.cap port 443 all interfaces, not promisc, disable dns, full packet size, verbos, up to 10k packets, write to a ram disk to avoid dropping, port 443 both tcp and udp just in case we try quic and time out when that fails.