s्मiley pants707 is experiencing an issue with a Facebook icon not displaying in the header of their community site, despite the link working correctly. jtbayly suggests the icon might be invisible due to a black icon on a black background, and recommends checking with Dev tools to ensure the icon is present and the color is being applied correctly.
vinothkannans provides a solution, referencing the Discourse GitHub repository. They explain that for “facebook” and “facebook-f” icons, adding “facebook-f” to the custom font awesome icons setting is necessary. smiley pants707 confirms that this solution worked, resolving the issue.
Hmmm. It still seems like it must be there though. Have you checked with Dev tools to see if it is there? And while you’re at it check the icon color is correctly being applied? Perhaps the FB icon is being overridden somehow.