The latest version in beta (v7.28) has improvements for the SHIELD Tube and allows 4K HDR and Dolby Vision content to successfully playback on the device.
Sadly the memory is the main issue, other devices like a FireStick have less but aren’t capable of the same 4K level of decoding (which requires a lot of resources to process). We are constantly improving our performance though, if you have a Tube be sure to install the latest beta.