Text styles in Visual Editor are now limited

On a client's site, suddenly in the Visual Editor the options in the text styles dropdown are limited. Client uses the "Address" text style, but it is no longer showing in the dropdown. Styles that do show are; Paragraph, Pre, Heading 1, Heading 2, Heading 3, Heading 4, Heading 5, Heading 6.

The "Address" style was available two days ago. No updates or changes were made to WP, the theme or plugins, the "Address" style just suddenly wasn't in the list.

I haven't been able to find anything online of other people with the problem of options missing. Come across a lot about adding custom styles, but what I'm trying to do is get back the missing styles from the list.

Happy to provide log in info.