The repositories at download.opensuse.org redirect, via Mirrorbrain, to a more or less local mirror server. It is either the mirrorbrain service or the selected mirror that is currently not working correctly.
I prefer to add a couple of mirror servers directly for each repository and then enable one that is working well. There is a list of mirrors at e.g: https://mirrors.opensuse.org/list/42.3.html
I would recommend choosing national academic services. Commercial organisations are able to publish numbers of “local” mirrors that can be in fact aliases to poorly maintained and poorly connected machines on the other side of the world.
If you are in Europe, ftp.gwdg.de is not always the fastest, but has had good reliability for many years. I also use the rsync service at anorien.warwick.ac.uk.
I am in south america, so many times europe an us mirrors do better job than local mirrors. I will try some us mirrors in the list. however, i kind of partially solve the problem manually changing repos uris to https instead of the http listed in the repositories wiki. then I can ref the repos. but when i update or try to install some packages, zypper tries to download from some http url and the the download fails again, even if the repo is congured with the https url. so the question is, is there a way of telling zypper to force https ?
i will try modifying the repos to some europe/us mirror and inform here. how do i know which repos are being used through redirection ?
When working in this mode, all changes in the database are automatically replicated to the mirror server. Thus, in the event of a failure of the main server, it is possible to quickly switch applications to the backup server