Links to YouTube, Facebook, G profiles not showing images

Per title; buttons to e.g. subscribe are showing images correctly, and the img src attributes point to valid files on the server as expected, but somehow neither Firefox nor IE is willing to display them on the page. There’s no error in the console I can see that would affect this.

Using 1.1.0.8 at https://ideaboxx.us.fujitsu.com/. Existing posts on the same topic do not appear to give any advice on resolving it.

https://www.ads-software.com/plugins/ultimate-social-media-icons/