CiviCRM Admin Utilities is a WordPress plugin that modifies and enhances CiviCRM's appearance and behaviour in single site and multisite WordPress installs.
@andyburnsco CAU doesn't actually do any menu rebuilding - it merely provides a link to the CiviCRM mechanism for doing so. I'd recommend that you open an issue with CiviCRM Core.
Using the link provided to rebuild menu within CAU doesn't rebuild menu in multisite.
I am trying to add in the icons for Civi; it is easy to see it isn't happening.
Is the best way to approach this is to rebuild in SQL? https://docs.civicrm.org/sysadmin/en/latest/install/multi-site/#build-the-navigation-links-for-new-domain