I like to sleep with the TV on and Prime Video decides to start playing random movies or series. Used to be I'd play a series like the Grand Tour, it'd get to the end of the episode list and once there were no more episodes Prime would stop playing anything and take me back to the page for the series. Now it decides that once the movie or series I'm watching is at the end to just play something else that I usually don't care about or would ever watch. Has anyone else had problems with this and is there another option besides turning auto play off?
Your Prime Roku app may be auto-play/auto-preview enabled (you'd know navigating the UI) - if its auto-preview enabled, you should be able to go into settings and disable it and autoplay.
Otherwise (if it isnt auto-preview enabled), you can try disabling autoplay in general to see if its changed as well:
https://www.amazon.com/gp/video/settings/playback/ref=atv_set_playback
Otherwise, restart your Roku and contact Amazon CS about the changed behavior.