4k thing may not be Netflix itself. There’s a ton of DRM that has to be working just right built into a lot of hardware and software. Many things can cause it to have issues and it’s designed to break if there is anything it considers abnormal. Problem is that it’s kinda, sorta new and hardware can’t be updated. Same issues happened with 1080p at the time. My PS3 HDMI port broke multiple times during warranty and then I gave up after it expired. Just the slight distortion caused by the defect made the TV and all the other devices decide it was being used to pirate content and so they refused to work. These days the devices are more stable and the media industry has stopped aggressively enforcing the DRM to be so aggressive. But they still are doing it with 4K. Any little bug in a driver, software, or hardware firmware and it falls back to 720p or 1080p if you’re lucky.