Packages listed for upgrade are not available

Hello!
I’m trying to zypper dup and I get a handful of errors about packages in the Science repository, which seem to be listed as available for upgrade, but are not actually so.
I checked from a browser and indeed they are listed but when clicking on them I get a 404 error message.

Retrieving: libmpdec3-2.5.1-6.22.x86_64.rpm ...........................................................[not found (367 B/s)]
File './x86_64/libmpdec3-2.5.1-6.22.x86_64.rpm' not found on medium 'http://download.opensuse.org/repositories/science/openSUSE_Tumbleweed/'
Abort, retry, ignore? [a/r/i/...? shows all options] (a): i
Warning: You have chosen to ignore a problem with download or installation of a package which might lead to broken dependencies of other packages. It is recommended to run 'zypper verify' after the operation has finished.
Retrieving: libsuitesparseconfig5-5.11.0-89.1.x86_64.rpm ............................................[not found (1.7 KiB/s)]
File './x86_64/libsuitesparseconfig5-5.11.0-89.1.x86_64.rpm' not found on medium 'http://download.opensuse.org/repositories/science/openSUSE_Tumbleweed/'
Abort, retry, ignore? [a/r/i/...? shows all options] (a): i
Warning: You have chosen to ignore a problem with download or installation of a package which might lead to broken dependencies of other packages. It is recommended to run 'zypper verify' after the operation has finished.
Retrieving: libcolamd2-2.9.6-89.1.x86_64.rpm ..........................................................[not found (368 B/s)]
File './x86_64/libcolamd2-2.9.6-89.1.x86_64.rpm' not found on medium 'http://download.opensuse.org/repositories/science/openSUSE_Tumbleweed/'
Abort, retry, ignore? [a/r/i/...? shows all options] (a): i
Warning: You have chosen to ignore a problem with download or installation of a package which might lead to broken dependencies of other packages. It is recommended to run 'zypper verify' after the operation has finished.
Retrieving package libccolamd2-2.9.6-89.1.x86_64                                    (44/278),  53.9 KiB ( 81.0 KiB unpacked)
Retrieving: libccolamd2-2.9.6-89.1.x86_64.rpm .......................................................[not found (1.6 KiB/s)]
File './x86_64/libccolamd2-2.9.6-89.1.x86_64.rpm' not found on medium 'http://download.opensuse.org/repositories/science/openSUSE_Tumbleweed/'
Abort, retry, ignore? [a/r/i/...? shows all options] (a): i
Warning: You have chosen to ignore a problem with download or installation of a package which might lead to broken dependencies of other packages. It is recommended to run 'zypper verify' after the operation has finished.
Retrieving package libcamd2-2.4.6-89.1.x86_64                                       (45/278),  54.8 KiB ( 87.4 KiB unpacked)
Retrieving: libcamd2-2.4.6-89.1.x86_64.rpm ............................................................[not found (366 B/s)]
File './x86_64/libcamd2-2.4.6-89.1.x86_64.rpm' not found on medium 'http://download.opensuse.org/repositories/science/openSUSE_Tumbleweed/'
Abort, retry, ignore? [a/r/i/...? shows all options] (a): i
Warning: You have chosen to ignore a problem with download or installation of a package which might lead to broken dependencies of other packages. It is recommended to run 'zypper verify' after the operation has finished.
Retrieving package libamd2-2.4.6-89.1.x86_64                                        (46/278),  52.8 KiB ( 82.7 KiB unpacked)
Retrieving: libamd2-2.4.6-89.1.x86_64.rpm ...........................................................[not found (1.6 KiB/s)]
File './x86_64/libamd2-2.4.6-89.1.x86_64.rpm' not found on medium 'http://download.opensuse.org/repositories/science/openSUSE_Tumbleweed/'
Abort, retry, ignore? [a/r/i/...? shows all options] (a): i
Warning: You have chosen to ignore a problem with download or installation of a package which might lead to broken dependencies of other packages. It is recommended to run 'zypper verify' after the operation has finished.
Retrieving package pcre2-devel-10.39-59.16.x86_64                                   (47/278), 299.7 KiB (279.9 KiB unpacked)
Retrieving: libcholmod3-3.0.14-89.1.x86_64.rpm ........................................................[not found (370 B/s)]
File './x86_64/libcholmod3-3.0.14-89.1.x86_64.rpm' not found on medium 'http://download.opensuse.org/repositories/science/openSUSE_Tumbleweed/'
Abort, retry, ignore? [a/r/i/...? shows all options] (a): i
Warning: You have chosen to ignore a problem with download or installation of a package which might lead to broken dependencies of other packages. It is recommended to run 'zypper verify' after the operation has finished.
Retrieving package libumfpack5-5.7.9-89.1.x86_64                                   (268/278), 915.9 KiB (  1.4 MiB unpacked)
Retrieving: libumfpack5-5.7.9-89.1.x86_64.rpm .........................................................[not found (369 B/s)]
File './x86_64/libumfpack5-5.7.9-89.1.x86_64.rpm' not found on medium 'http://download.opensuse.org/repositories/science/openSUSE_Tumbleweed/'
Abort, retry, ignore? [a/r/i/...? shows all options] (a): i
Warning: You have chosen to ignore a problem with download or installation of a package which might lead to broken dependencies of other packages. It is recommended to run 'zypper verify' after the operation has finished.

About a week ago I got a similar problem with a package in the games repository, which I wasn’t using on this machine, so I deleted it and proceeded with the upgrade because I thought it was just a temporary thing and nobody in the Games subforum seemed to give it any relevance.
However, now there seem to be a few more packages with the same problem (at least for me). Any ideas or suggestions?
Thanks in advance.

I switched to a mirror and zypper-dupped successfully, but I was wondering if anyone else was having the same problem.

I’ve never used the Science repository, but with others, it’s not been an unfamiliar situation. Sometimes repos just haven’t fully sync’d before being put into use. Forcing a particular mirror for a particular package often works. Other times, just waiting some period of time for sync to finish is the best way forward. Another option is finding the package via web browser, and fetching it into /var/cache/zypp/*, then retrying.