RN 10200 & kodi. Movies don't play.

Is it possible something is wrong with the connection speed?  What connection speed do the LED's on the Kodi box, router(s)/switch(es), and NAS show?  Have you made any changes there?  A slow connection might not be noticable for browsing but certainly would viewing HD content, and in a way much as you describe.  Music would probably still work OK with a slow connection, so try that, too, just to see.