I've begun having random issues with both of my Nexus players in the last couple weeks. Casting is very hit or miss, sometimes it won't show up on my phone as a cast device, other times screen will just go black when I cast a video.
Netflix and plex have started randomly quitting. It doesn't give a force close dialog, simply closes and loads the launcher. It's almost like there is a memory leak issue because the suggestion bar is reloaded too implying the launcher was purged from ram. Sometimes Netflix will play for a while with no issues, others times less than 5 minutes will play.
Just today the plex user data seemed to have been erased and had to sign in to my account again.
System and apps are up to date.
Update 2/3/17: it's only been getting worse. The remote has started becoming unpaired. Going to pick up a Mi Box this week.
I get the same behaviour with Netflix suddenly quitting. Plex keeps giving errors that it's losing connection to the server. Unfortunately I have no solutions for you.