Steps to reproduce:
Set up a search in Scroll Viewport
Create Pages Verfügbarkeit, Verfügbarkeitsanalyse and Verfügbarkeitstest
Search for Verfügbarkeit
Yield all three pages that contain the name "Verfügbarkeit"
While Confluence shows all three pages, Scroll Viewport isn't able to find any of the pages. Only when looking for the exact page name, it will yield the desired page.
Manually enter "*" after the search value to get all pages sub-matching the string.
If your theme is based off the webhelp theme, you can simply fix this with the following change:
In assets/js/scroll-search.js on line 10, change the line from