What do you see in the Theme Customizer in Appearance -> Customize -> General Settings -> Site Identity -> TAGLINE?
Sounds like a Caching Problem. Please try the following steps:
- Clear your Browser Cache
- Clear Cache Plugin Data (W3 Total Cache, WP Super Cache, ..)
- Clear Cache from Web hoster (for example Siteground have a Clear Cache Button in CPanel)
- If you use a CDN like Siteground Purge Cache also here