Unable to repair broken Yum repository

We have been using Nexus to proxy OpenSUSE RPM repositories.

This has worked fine up until now, when we got an invalid repository.

[2021-06-17T06:47:39.919Z] Repository 'repo-update-oss' is invalid.
[2021-06-17T06:47:39.919Z] [repo-update-oss|https://nexus.company.com:8443/repository/OpenSUSE_Leap15.2-update-oss/] Valid metadata not found at specified URL
[2021-06-17T06:47:39.919Z] History:
[2021-06-17T06:47:39.919Z]  - File './repodata/8ae
3296bc61c3424ed4aaa9029f2ced8c39e385e18a7cadb7121a20ffbe0b925-deltainfo.xml.gz' not found on medium 'https://nexus.company.com:8443/repository/OpenSUSE_Leap15.2-update-oss/'
[2021-06-17T06:47:39.919Z]  - Can't provide ./repodata/8ae3296bc61c3424ed4aaa9029f2ced8c39e385e18a7cadb7121a20ffbe0b925-deltainfo.xml.gz

How can this file just be gone from the repository?

I have tried everything to fix it:
Invalidate cache
Rebuild index
Deleting RPMs
Deleting repodata

But the repository is never being rebuilt.

I tried to create the task Repair - Rebuild Yum repository metadata (repodata), but something in that is broken, because I cannot select a Yum repository. The drop down list for repository will not open up (or is empty).

Edit:
The repodata eventually came back after I deleted it, but it does not contain any file other than repomd.xml and repomd.xml.asc. The repodata file is referring to files that are not there.

Edit2:
I deleted the repository i Nexus, then recreated it.
After Nexus has created repodata, there is now also one “-deltainf.xml.gz" and one "-primary.xml.gz”.
However now, it fails with refresh. It complains about wrong file size

Retrieving repository 'repo-update-oss' metadata ...............................................................................................................................................[error]
Repository 'repo-update-oss' is invalid.
[repo-update-oss|https://nexus.company.com:8443/repository/OpenSUSE_Leap15.2-update-oss/] Valid metadata not found at specified URL
History:
 - Downloaded data exceeded the expected filesize '567.4 KiB' of 'https://nexus.company.com:8443/repository/OpenSUSE_Leap15.2-update-oss/repodata/8ae3296bc61c3424ed4aaa9029f2ced8c39e385e18a7cadb7121a20ffbe0b925-deltainfo.xml.gz'.
 - Can't provide ./repodata/8ae3296bc61c3424ed4aaa9029f2ced8c39e385e18a7cadb7121a20ffbe0b925-deltainfo.xml.gz

This file is actually 2.8MB showing in Nexus.
The correct size is actually 567KB from OpenSUSE, so why is it 2.8MB in Nexus?
https://download.opensuse.org/update/leap/15.2/oss/repodata/8ae3296bc61c3424ed4aaa9029f2ced8c39e385e18a7cadb7121a20ffbe0b925-deltainfo.xml.gz

I don’t think we support the deltainfo file, at least I see no references to it in the code. Possibly this is something OpenSUSE has started using recently.

It must be very recently then. The Yum Proxy has worked fine up until now.
Found an issue that seems related to this, but it is an old issue.