I've been having major issues playing content on my Roku 3. Whenever I try to play something around 7mb/s or more, I get lots of pauses to rebuffer. I'd say it happens 2 or 3 times per minute. Which makes it unwatchable.
I hadn't used Plex in about 3 months (travel and relocating to a different state). I updated to PMS 1.7.2 as soon as I unpacked all my hardware and got my Synology set up. I'm running DSM 6.1.2-15132 on a DS1815+. The Roku player version is 4.4.1 according to the settings screen. Both the Roku and the Synology are wired via CAT5E to a Netgear Nighthawk X6, so they have gigabit connections.
A few days ago I tried to play a movie at about 10.9mb/s average and first noticed the rebuffering. It was the first time I've used Plex since the beginning of March. So I switched from the 1080p version to a 720p version at about 6.1mb/s average and it played fine. Last night, I tried another movie at 7.5mb/s average and it did the rebuffering thing again. When I back out of playback mode, I get the message that says my network isn't fast enough, which can't be the case.
I flipped over to my old Nexus Player running Plex 6.1.1.656 on Android 7.1.2. The Nexus Player is on WiFi, yet it played back the whole movie without any stuttering.
In both devices, the players are set to Auto Direct Play with no subtitles. The movies have h.264 video tracks and DTS audio tracks. Log files are attached. I played the same movie for the first 5 minutes on each player back to back for comparison. Something seems broken in the Roku player.