If you pause a song in any of your devices, it still stays in the Now Playing list. I can have things in the now playing list for hours as people pause things and go about their business. The Now Playing list should be for things that are being actively played - having items sit in the list on pause is useless.
The same thing happens if people pause things on the Roku and then switch to another HDMI port (e.g. to the Cable tuner) without exiting the Plex app. It'll sit in Now Playing on pause until they come back in to the Roku or, I guess, something somewhere times out.
Remove items from Now Playing when paused. Or, at least, give us a server option to not display items that are Paused in Now Playing.