Recently, we merged a PR that used some features from "unstable" ENet. Unfortunately, this meant that using system-provided ENet (which is usually on the latest release) when building Dolphin would cause a compilation error.
Because of this, FifoCI on some machines broke for several days. Because FifoCI only reports failures when Dolphin crashes while playing back a FIFO log, nobody noticed the failure.
If FifoCI build failures were listed in the PR checks, this wouldn't have happened.