Cannot upload files with webdav: no permission

I use Nextcloud (installed with Nextcloud-AIO) as storage for my SeedVaultBackup. The whole backup is successfully uploaded, except two files: .backup.icons and backup.metadata. I looked into it and these are the errors I got in the log. They seem to be related.

It is weird that only these two files aren’t uploaded and the rest is…

webdav
Exception Error while copying file to target location (copied: -1 byte, expected filesize: 15157 bytes)
Exception Error while copying file to target location (copied: -1 byte, expected filesize: 408631 bytes)

PHP
file_put_contents(/mnt/ncdata/<redacted>/files/.SeedVaultAndroidBackup/1717117045675/.backup.metadata): Failed to open stream: Permission denied at /var/www/html/lib/private/Files/Storage/Local.php#339

file_put_contents(/mnt/ncdata/<redacted>/files/.SeedVaultAndroidBackup/1717117045675/.backup.icons): Failed to open stream: Permission denied at /var/www/html/lib/private/Files/Storage/Local.php#339

Is this a SeedVault issue or a Nextcloud issue?

I think you must exclude dot-files.

that is not really an option as they are vital to the back-up