Buffering Issues: Unable to watch movies

Just set up a RPi 2 with Rasplex, latest build. Plex server is on latest version as well. Problem is that movies at 720p or 1080p are buffering every 3 seconds.
It plays 480p ok.
Connection is wired Ethernet.
This is a default install, no other modifications have been made.
Watching the same movie on an iPhone or iPad works without a hitch.

Can you please help figure this out?

What kind of system is running your PMS server, and is that server on the same LAN as the RPi2 ?

My own RPi2 has no problems playing 1080p movies, when using wired Ethernet. Even my RPi1 can do that.
The most critical factor is not the video resolution, but the overall bitrate and also the CODEC complexity.

eg: An RPi1 will NEVER be able to natively handle high bitrate videos using HEVC/x265 CODEC.
An RPi2 might be able to do it for reasonable bitrates, but as yet no suitable decoder lib exists…
So such videos have to be transcoded by the PMS server (assuming it has the processing power).

But even an RPi1 will handle x264 videos at bitrates up to 20Mbps over wired Ethernet.
And an RPi2 should be able to go FAR beyond that. My own RPi2 has no problem direct-playing any of my videos in original blueray format, some of which exceed 40Mbps. And tests show it can go much higher too.

So tell us more about your server-client setups, and maybe we can figure out what’s wrong there.

Best regards: dlanor