It's likely there's an unrelated error happening (usually database connection issues) which means XF can't load the active addons from the database, which means it doesn't load the UI.X addon and doesn't define these functions. The same thing would happen with other addons that use custom properties or functions in templates, it's just more noticeable with UI.X due to the number of uses of the custom functions. The errors will be in batches all happening at the same time, if you go back to the first error at a particular time, it will probably be something to do with a database connection.
