The whole thing started like a half a year ago, when pacman started throwing 404 errors on random package downloads, thus halting the whole package installation / update process. Executing
pacman -Syyu, changing the mirrors in the /etc/pacman.d/mirrorlist never solved it, though it eventually went off in a couple of days, emerging on random other packages here and there.
To clarify, I enabled different mirrors by uncommenting them (removing the
/etc/pacman.d/mirrorlist, choosing random mirrors from all around the world and I caught the same error on random packages, regardless of country or mirror rank.
Digging the issue, I've realized the requested package file was always version-wise older than its updated counterpart on the server (mirror): i.e. pacman requested mesa-21.1.1-1-x86_64.pkg.tar.zst as per recently updated official extra repository (namely
pacman -Syy mesa) vs. mesa-21.1.2-1-x86_64.pkg.tar.zst located on the mirror, so the problem is that the repo is out-of-date rather than mirrors (vice versa would be totally understandable, as official repos are more or less centralized contrary to the decentralized mirror network), thus requesting the older version (already removed from the mirror in lieu of the more recent version) expectedly throws an 404 File Not Found error.
Is there any explanation to this issue, and is there any way to fix it?