With Add Media in post or page you have the choice to “Create Gallery”, It has been found from titcrea and tompoezie that the making of a new gallery is no problem.
But, modify an existing gallery cause problems when you want to update those.
The gallery updates (Update gallery) works but then update the page/post the changes are not saved.
We seek for a final solution.
But in the meantime you can use a workaround.
In visual mode:
Once you have adjusted the gallery and choose “Update gallery” you’re back on the post/page. Now put the cursor in the editor outside the gallery, to activate the text field and update your post/page then the changes will be saved.