We set up the sync and it seems to be working fine, except a bug where it sets the username and nickname as similar in Wordpress, and that makes the username invalid in Wordpress.
It works, but if you try to change anything for example a users role, you get the error message and the change doesn’t go through
Are you syncing accounts by enabling the ‘Create or Sync Discourse Users on Login’ option? All it is doing is sending user data from WordPress to Discourse. The only field it updates on WordPress is the Discourse Username field. This field is only used by the WP Discourse plugin, so it shouldn’t be causing a problem.
I think that by default WordPress sets the nickname to the same value as the username field. Do you have the iThemes Security plugin installed on your site? The only reference I can find to the error in your screenshot is for sites that are using that plugin.
Just in case anyway comes along and sees this again, it was the ithemes module “system tweaks” which causes the issues, if you disable that, should work. Seems “system tweaks” in ithemes security modifies server config files