Outside collaborators see an error when clicking on the invitation link, but the repository itself is created and available via link

Everything worked fine until the new year, but recently, when outside collaborators clicked the invite link, they started seeing an access error screen ("Repository access issue. You no longer have access to your assignment repository. Contact your teacher for support"). However, their fork is created in the classroom, and they can access fork via the link and make commits. All their repositories are private.

まず、private assignment repositoryを使って外部コラボレーターへの招待フローを再現し、次に招待リンクの結果を、機能するrepository fork linkと比較します。招待とrepository accessを担当するGitHub Classroom CLIの経路を追跡します。外部コラボレーターがアクセスエラーなしで招待リンクをたどり、作成したforkに到達できれば完了です。

索引モデルが issue の本文から書いたものです。