Share with Anyone, doesn't require sign-in now not working

We've been creating Stream recordings, guiding people how to use various systems, and posting them on the University (external) help site. I know we can't embed Stream videos for externals/guests to access but the URL links have been working fine for us up until a few days ago. 

Now, when someone clicks on the URL, the video opens but they are prompted (browser pop-up) to sign in. If they close this window down, it'll reappear two more times. 

If they are accessing on mobile, they cannot close the sign-in window. 

Has anyone else seen similar behaviour? We're on Stream for SharePoint and the sharing location has permission to "Share with Anyone, doesn't require sign-in"