InRelease lists files on which apt fails when on local repository

On Focal:

Please verify that ftp://www.archive.ubuntu.com/ubuntu/dists/focal/main/dep11/ does not contain a file called icons-48x48.tar - though the InRelease file (ftp://www.archive.ubuntu.com/ubuntu/dists/focal/InRelease) lists one.

When the sources.list is configured for http, the missing file is ignored and apt works fine.
When the sources.list is configured for a local folder, apt fails:

Failed to fetch file:/... File not found.
E: Some index files failed to download. They have been ignored ...

Still it is not ignored cause apt now fails to install any new package.

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Note that, in order to test this I setup an apache2 for a local directory listing. So apt is always accessing the same repository. Once with http: (which succeeds) and once with file:

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So from my perspective the handling of missing files (from InRelease) is different when using http: and file:
Either apt allows missing files from a local repository, or the InRelease file shall be corrected.

Regards!