See attached screenshot.

This happens for all detail subapps (pages app, asset app, contact app, inplace-templating, ...), but not for all entry. For example in pages app - "subsection-articles" page has title every time, but "article" page never.

It happens for entries which have space in title, but only when they are open from browser app directly. If page without space in title is opened then tab label is available and then if you navigate (in same instance of detail subapp) to the page with space in title then label is correctly shown.