Stopped working tmptitle – Draft

Postie suddenly only creates a draft post with post title tmptitle which it stores as a draft and it replaces the post content with tmpPost. It also no longer deletes the post from the Inbox, although it is set-up to do so.
If I change the settings to Allow anyone to post via E-mail, it seems to work fine, which means it doesn’t recognize any of the allowed roles (Editors and Admin) as valid users.
Even posts sent from Authorized e-mail addresses end up as drafts with titles and content stripped.
It is the latest version 1.9.57
How can this be fixed?