Most likely what happened was that when you changed the permalink, the content editor was in visual mode, and saving the change also removed some of the HTML that was needed for the ionicons to actually appear. When I looked at your site, the code that would have told it which icons to show was missing.
You can probably roll back the content using a previous post revision, if there is one available. This tutorial should help, if you don't already know how:
http://www.wpbeginner.com/beginners-guide/how-to-undo-changes-in-wordpress-with-post-revisions/
