When "idle" isn't idle: how a Linux kernel optimization became a QUIC bug The open source implementation of QUIC, quiche, has stumbled upon an intriguing issue that highlights the complexities of congestion control algorithms.
A recent investigation by Cloudflare's team revealed a bug in CUBIC, the default congestion controller, which causes it to permanently pin its congestion window at minimum and fail to recover from congestion collapse events.
The root cause of this anomaly lies in CUBIC's logic, based on several assumptions that have been revisited over the years.