See #4059 / #4042

Several plugins (and themes...) use the enter_title_here filter to display their own title "placeholder" (note: in the classic editor it's actually a <label> element) for their custom post types. When the passed string contains a special character and the string gets escaped, The placeholder used in Gutenberg displays an encoded character.

For example, see in the screenshot below the "Add New Testimonial` screen from Jetpack:

Worth also noting that translations might add quotes or ampersands etc. to the original English strings.

Escaping is a good practice for HTML but an encoded character is just displayed "as is" in Gutenberg. Ideally, Gutenberg should handle these cases in some way.