Plex having a hissy fit moments before the end of every movie

JustAnotherSaver

So as i started out with Plex i was streaming (correct term? Possibly not) blu ray copies from my PC to the downstairs TV which is all connected to my router via cat6 cable and it would end up buffering. Some movies were better than others as far as buffering went but most would buffer somewhere along the line.

Lately that seems to have stopped. I select the 5.1 audio usually instead of 7.1 stereo. I'm not saying this will make a difference or not, i'm just saying what i'm doing differently. I'll still select subtitles because i'm deaf ... according to my wife. For the video playback i've been selecting 10 or 12 Mbps rather than full quality.

And then the movies generally play absolutely fine throughout ....... until they all get to about 30 minutes from the end of the movie. They can be 2hr - 2hr30min kind of movies but when i'm about 30mins from the end the screen blanks out, i get the 3 yellow dots on the TV and then it times out (replace with correct terminology if you wish).

I go to check on the PC, it hasn't gone to sleep or anything. I go back downstairs and fire up Plex again, resume the movie and it initially begins to buffer for a few minutes before either A) then playing fine or totally shutting down, the TV then throws up a HDMI 1 sign in the top corner to which i have to then go in to Plex once again, load up the movie and resume once again, it'll buffer once again for a while and then it finishes the movie smoothly.

For some reason it seems to have a bit of a hissy fit in and around the 30 minutes from time marker. May be 20 mins, may be 50 mins but it's in and about that 30 minute area.

Why?