yum コマンドが "Curl error (37):Couldn't read a file" - "Issue while fetching content using Custom or third party repositories" で失敗する

Issue

• システムが適切にアクティブな Red Hat サブスクリプションで登録されているにもかかわらず Yum コマンドが以下のエラーで失敗する

# yum repolist -v
Loaded plugins: builddep, changelog, config-manager, copr, debug, debuginfo-install, download, generate_completion_cache, groups-manager, needs-restarting, playground, product-id, repoclosure, repodiff, repograph, repomanage, reposync, subscription-manager, uploadprofile
Updating Subscription Management repositories.
YUM version: 4.7.0
cachedir: /var/cache/dnf
Red Hat Enterprise Linux 8 for x86_64 - AppStre 2.6 MB/s |  57 MB     00:21
Red Hat Enterprise Linux 8 for x86_64 - BaseOS  4.7 MB/s |  60 MB     00:12
LocalRepository_BaseOS                          0.0  B/s |   0  B     00:00
Errors during downloading metadata for repository 'LocalRepo_BaseOS':
  - Curl error (37): Couldn't read a file:// file for file:///mnt/BaseOS/repodata/repomd.xml [Couldn't open file /mnt/BaseOS/repodata/repomd.xml]
Error: Failed to download metadata for repo 'LocalRepo_BaseOS': Cannot download repomd.xml: Cannot download repodata/repomd.xml: All mirrors were tried