Sorry, I just saw this thread. I also have same issue with Netflix...Exit option doesn't work.
Ver 7.2.5 on FS4K
I usually use my Onkyo remote to operate FS.
From last fewdays, To exit Netflix, I had to pickup FS remote everytime (by pressing Home button)
But as a workaround, since Firetv Routines launched, I created a routine in Alexa to go to Home Screen, when I say 'Home' to my Echo devices