Conflict with admin nav menu editor

Thank you for reporting this.

What plugin are you using to assign icons to each menu item? Can you contact the developers and show them this thread?

Restrict User Access plugs into the nav menu in the admin panel in order to add the Levels input, so you can display items to selected access levels.

This might be the cause of the incompatibility, however, it does it in a similar way as these plugins:
https://github.com/kucrut/wp-menu-item-custom-fields
https://www.ads-software.com/plugins/nav-menu-roles/
https://www.ads-software.com/plugins/menu-items-visibility-control/

All these plugins, including Restrict User Access, adds the action wp_nav_menu_item_custom_fields that developers can hook into.