If another player connects and the BuzzTV 6 app does not, the box is fine. The two are almost certainly being given different kinds of login.
Providers issue more than one set of details and they are not interchangeable: an M3U playlist link, an Xtream Codes (XC) URL with username and password, or a MAC portal tied to your box. Another app may be running on an M3U link while BuzzTV 6 is set up as XC. Same subscription, different door.
What to do:
Still stuck? Email cs@buzztv.com with a photo of the white label on the underside of your device, which we use for utility and system checks, and tell us what you see on screen. Support is Monday to Friday, 10:00 to 18:00 Eastern.