Some 4K UHD content plays for 20 seconds then snow or static (Roku Ultra)
Twice I've tried to play recently-released 4K UHD content through two different (Apple TV+ and Prime Video) apps on my Roku Ultra and after 15-20 seconds of good video, the screen turns to snow. The sound & subtitles continue unaffected. I can restart the video or resume the video and the same behavior occurs - 15-20 seconds of good video, then snow.
The problem only seems to happen on very recently-released video content - yesterday, it was trying to view the film Spencer using the Apple TV+ app. I am able to successfully view other 4K content using both of these apps.
I've tried rebooting the Roku, removing & reinstalling the apps on the Roku, and using a brand new high performance HDMI cable with no change. The TV is an LG OLED77CX that was purchased in March, 2021.
I suspect it is the Roku because the problem occurs with two different apps, and because I can AirPlay the video from the Apple TV app on my phone directly to the TV with no problem at all.
Any other suggestions for things I might try? Thank you.