Steps to reproduce the issue

On a desktop, open an article (or a module) to edit it.
Narrow the width of the browser so the screen width is about 900px
See the sub-head menu:

Click the 'Save' button (It's not necessary to change the article).

Expected result

The article is saved but the sub-head menu should still be visible.

Actual result

The sub-head container has disappeared:

In fact, if you narrow the screen to its minimum, the menu disappears without the 'save' option being applied first.

The only way to retrieve the menu is to pull the browser wider.

The same issue happens with a new article or module except that the sub-head container does not appear at all on narrower screens.

System information (as much as possible)

J4.0.3 fresh install onn 08/10/2021

Additional comments