Recently we noticed that when external users are browsing our SharePoint sites the SharePoint header bar with the tenant logo, search box, and account link is not loading. The logo never appears, the color is using the default SharePoint blue color instead of our theme color, and the account link in the top right doesn't appear.
I looked at the browser dev tools console and saw the following request is throwing a 400 error. I'm not sure if it's related but it's not throwing the same error when an internal user views the same page. There is no UPN value at the end of this URL but there is for internal users. Is that an issue and what would cause that?
Failed to load resource: the server responded with a status of 400 ()
Here is a screen shot of the header that an external users see. You can see that there's no logo, it's the wrong color, and there's no account link in the top right
Here is a screen shot of what an internal users see. I blocked out the logo for privacy reasons. The color is correct and you can see my account link in the top right
Here is a screen shot of a message that is now all the sudden appearing for users viewing the site on mobile in Safari. You can see the wrong blue bar is loading at the top, as well (I blocked out the content above and below the pop up for privacy reasons)
It appears that something is not allowing the header to fully load for external users and the only error that I'm seeing is the one I put above. Anyone having the same issue?