The way VisualEditor handles links with square brackets, but no explicit anchor, can be confusing. These links are generally discouraged on English Wikipedia, but still occasionally used.
An example is https://en.wikipedia.org/w/index.php?title=User:Superm401/Sandbox&veaction=edit&oldid=564175896 . The wikitext for this is just [http://example.com], which renders as a linked  (or whatever number it is in the page)
However, you should edit the latest version of a page for testing this. When you edit an oldid page, you won't be able to reproduce the "Save page" disable behavior I mention below.
VisualEditor lets you backspace to remove the characters one by one, which does not really reflect the model of how the link works. After one or more is removed, "Save page" un-greys. However, when you go to review the changes, it says, "Could not start the review because your revision matches the latest version of this page."
It does let you remove the link entirely, but to do so you need to explicitly remove each character (not just backspace once to delete the whole thing).
Do a fresh load of the edit page (separate test). Then, click the chain icon next to the link. Then, press enter twice to exit the link dialog. This time, review changes works. The wikitext becomes:
It probably should not change the link if you simply enter the link dialog and press enter without changing anything. Also, forcing it to text like this is inconsistent with what happens if you delete the right bracket (see above).