The fonts of .display-* and .lead bootstrap css classes does not work on some devices.
I know this isn’t a hosting problem, but how can I avoid this problem? (load the fonts as a webfont maybe?)
There is a general structure as to how fonts work with browsers:
You load specific font types with a specific font weight into the document. If you use a font weight that isn’t supported by that font, the browser will try to automatically re-render the font to that weight. Thats why you get the fuzzy font issue.