The recently introduced Font Awesome SVG is a wonderful tool to display fascinating icons on web pages. However, in its default configuration, it interferes with the icons of Wishlist button and they may not function properly. Commonly, a question mark (?) or Exclamation mark (!) gets displayed instead of the selected icon.
In order to fix this, you need to set the observeMutations property in FontAwesome configuration to false.
In case there does not exist the configuration option, add the following code in the <head> section of of page, just before including the all.js file.