Sorry for the delay. I’ve been away at a sports tournament, but this is covered in the FAQ:
https://wordpress.org/plugins/nav-menu-roles/faq/
You should contact the author of the conflicting plugin/theme to ask him/her to view my faq in order to add compatibility.
You can also try to patch the plugin yourself by reading the “Patching Your Plugin/Theme” section of the FAQ.
Thanks for your advice, there is no start_el() function in FA 4 menu plugin, but there is in the AGP font awesome collection plugin, which it works with. I added the patch to both walkers in this plugin, but it didn’t fix the problem, any other ideas?
Looks like Font Awesome 4 menu doesn’t replace the menu Walker so there is no conflict. The menu options are merely the CSS classes, so be sure that it checked under Screen Options. Otherwise, please contact the Font Awesome 4 Menu authors for help.
