Update 1: 2019/10/14 12:38am PDT
Vudu, one of the apps affected by the 4K playback issues, now says that the problem is fixed on the Shield. You need the latest version of the Vudu app
Last month, a problem with 4K playback surfaced on Nvidia’s Shield TV. The issue affected VUDU and a few other unnamed services, and only occurred when using their native apps but not when casting to the Shield.
[Update: Vudu fixed] Nvidia rolls out minor update to fix the Shield’s 4K playback issues was written by the awesome team at Android Police.