I bought a Raspberry Pi 3 Model B+ and followed this guide (https://thepi.io/how-to-set-up-a-raspbe ... ex-server/) on how to turn it into a Plex server but it's performance is awful. I have it connected via Ethernet and a 1 terabyte hard drive holding all of my movies and shows. However it buffers a lot and sometimes drops the stream all together when I'm accessing it via the Plex app on my Roku in my basement, and on my desktop, which it located right next to my raspberry pi. When I tried it on my parent's Roku TV it streamed fine. I tried it again streaming The Last Jedi on my Roku TV and on the Roku device in the basement. The one streaming on the TV ran without a hitch using at most 23% CPU usage but on the Roku device in the basement it was constantly buffering and used 99% CPU usage. I don't know why it runs perfectly fine on the Roku TV but not on the Roku device or my desktop.
What did I do wrong? Is it the files themselves? The network? is there something else I need to do to the raspberry pi? I included a picture of the Media Info of The Last Jedi file I tried to stream.