After upgrading to curl 7.79.0 (from 7.78.0) I'm seeing connection stalls and dropouts in Arch Linux's package manager (pacman). The issue is reproducible when using Basic authentication against a HTTP/2 mirror. (It doesn't happen without Basic auth.)
Bisected this to commit 3cb8a74. I don't have a reliable reproducer yet; I used repeated pacman -Syy calls for testing and the issue usually occurs within the first few invocations. Each pacman -Syy call downloads 5 repositories concurrently (a few MiB each) using libcurl's multi interface.
No tangible error messages other than Operation too slow. Less than 1 bytes/sec transferred the last 10 seconds and/or transfer closed with 5472421 bytes remaining to read. Sorry for not providing a reproducer outside of pacman; I'll update this issue if I manage to come up with one.
Regression from 3cb8a74 (releasde in 7.79.0). That change moved
transfer oriented inits to before the check but also erroneously moved a
few connection oriented ones, which causes problems.
Reported-by: Evangelos Foutras