Several icons invisible

Most icons are invisible on freecodecamp forum, however the mouseover highlights the button and displays text. It is likely blocked by the firewall. Adding text/color to the buttons makes them visible. Is this a common problem?

I think the bootstrap icons source may be blocked by the firewall, but I can see the text that is next to the icon, the color change grey mouse over, and the text that appears when mouse over. It does make them somewhat hard to find though.