Social media icons not visible

Hi, I’ve already done some research in the forum but still haven’t found a solution. I installed the plugin Ultimate Social Media Icons.

Answers to questions in plugin:
1) facebook, youtube, instagram
2) facebook all 3 boxes checked, youtube first box checked – visit
3) show them via a widget (I have also tried shortcode and placing shortcode via customizer, didn’t work either)

I drag&dropped the USMI-widget in the footer section, the title is visible, but not the icons. I have tried suggestions from other forum posts: deleting cache, changing size of icons in question 6). No success.

As this is not my own site I can’t post a link.
Thanks for ideas!