I keep loosing social icons in header/footer when using IE

Hi,
I keep loosing the social icons (font awsome) in header/footer when viewing website in IE 11 (11.0.16) I have reinstalled twice now and everything looks fine with a fresh install but then all of a sudden … icons are gone. They are click-able but invisible.

Everything looks fine in Chrome (win7) and on Safari (iphone) and Google (Android). But icons are missing in IE11 (win7) and Chrome (Android)

Any suggestion?

Brgds
Jakob