My guess is that a plugin called HootKit which is also loading Font Awesome (icon library) is clashing with Ultra which loads the same library. We can find a solution but for the moment, please, try temporarily deactivating HootKit and then test the issue to see if it resolves.
If you need the plugin in question, you could perhaps ask the developers if they could send you a snippet to dequeue Font Awesome from their plugin. If they can’t help, please, let me know.