I had similar problems that involved crashing, no video, only audio, sparkles, etc. However, I may have found a solution. I believe I encountered these problems when I switched directly from my Sony television's (XBR 900E) apps to the ATV 4K; that is, waking up the ATV while my television was on. Instead, I now use my ATV remote to simultaneously wake up the ATV and the television. There is a slight delay as the television switches to the enhanced HDMI 2 port, but then everything seems to work fine. When I'm finished viewing, I click on Sleep Now , which turns off both the ATV and the television.
I'm not an expert on these matters, but from researching the problem on the net, I think these issues may be related to the ATV's making a "handshake" with the television's HDMI port so that they can work in sync.
Like many of you, I've gone through switching settings, changing cables, rebooting, etc. I hope this helps.