Hello,
I use KPN NL (AS1136) and sites behind Fastly CDN frequently experience 6-30 sec stalls when accessed via HTTP/3 over IPv6. HTTP/2 works perfectly, so I suspect there is some issue specifically with my ISP and the Fastly POPs it is hitting, perhaps related to bad ECMP hashing with UDP / IPv6 and missing QUIC stateless resets?
I initially suspected this to be a Chrome bug, however with the problem reproducing exclusively on Fastly-backed hosts, I suspect it might be something on Fastly’s side that needs fixing so I thought I’d post here as well. Please find the full original report including netlogs and tcpdump output at Chromium
Happy to provide any additional info that’s needed.