FYI, I realize that the YouTube running on your Chromecast is not the
same YouTube app running on your phone but it appears that something is
failing on the phone app which then signals the app running on the
Chromecast to terminate.Another test you ...
I had the same problem (with both of my Gen 2 Chromecast units) that
started recently (past several months). I believe it is caused by a
number of factors which may be unique from phone to phone, but give this
a shot..For the record, I'm using a One ...