My Mi 4X tv is a 100% android 4K tv with L1 widevine support. I also have 100 Mbits internet speed yet I am not able to watch content at 4K/ UHD. The max quality it shows on amazon prime is HD, so I am assuming it is 720p. Any guesses about what I can do?
By the way, I can easily play 4k videos on Youtube.
I'm not familiar with your box, but I can say that even with my firetv it can sometimes be hard to get it to trigger 4k. It seems like sometimes they limit the quality if it's peak watch time and their servers are a little overloaded. Also HD on the video usually means 1080p.
I have the same TV and the same problem. Haven't been able to figure out.
What about Netflix? Your device may not have the necessary certificates.