There was a bug that was fixed in earlier versions -- I just tested in my lab on a fresh box, and it works OK, so I'm assuming your box was upgraded from an older version?
If so, you're seeing the bug because your old config is still there. If this is for one of the pre-built error pages (e.g. Posture, Jailbroken, etc.), reset the config for that web page:
CPGuest > Config > Pages > Web Pages > (click yours) > Reset to Defaults
From a code-perspective, this is simply changing your [old] code from a <span>...</span>:
<span class="fa fa-cogs" style="font-size: 200px; color: #F5821F;"></span>
And changing it to an <i>...</i>:
<i class="fa fa-cogs" style="font-size: 200px; color: #F5821F;"></i>
E.g. the <i>...</i> will be the snippet that works fine with Galleria.
Let me know if this is resolved, or if you still see any issues?