Reply To: Header Image

Dear Torsten,
Such issues are common for the iOS devices as Safari browser still does not support background-attachment: fixed; property. But it should not appear on the Android devices.
But you can add the following code in Additional CSS. It will solve the issue.
Appearance > Customize > Additional CSS

@media(max-width:767px){
   .inner-main-title {
      background-attachment: scroll !important;
  }
}

(Note: It will change in all mobile devices)

Best Regards!