Ds918+ as Plex server not playing nicely with fire tv

I haven’t had issues in past but recently we went to play a Blu ray version of a movie to the fire tv and it was taxing the 918+ cpu. The firetv was able to play Blu Rays before with no issue. Everything is on the same network although the fire tv is WiFi of course. I could play the Blu ray to my iPhone 8 with no issues and to the desktop with no issue although the desk top is wired to same network the 918 is wired too. Not to sure what the issue could be. This happened with multiple Blu Rays.