Are you using a variable font? I ran into the same problem with a variable font (League Spartan), but then I added just the bold version (League Spartan Bold) as a new font and now it works great!
This is the old code, using the variable font, which gave me the triplicated look on mobile (iPhone):
h1, h2, h3, h4 {font-family: 'League Spartan'; font-weight: 700 !important; }
Now I'm using this code, using the bold font:
h1, h2, h3, h4 {font-family: 'League Spartan Bold' !important; }
Hope this helps!
