Hello,
This message appears only when the theme has been updated and plugins have not. Sometimes after theme and plugins have been updated the message may still remain due to cache plugins or settings and I just do not have another more professional suggestions for such a case. Just update the plugins and clean the cache.
In addition for you to know and inform your customers sometimes just after the theme update, the site looks like a big shortcode. Your customer should not worry just reload the page and clean cache such may happen for a second one after the update provided third parties plugins.
Best Regards