Frequent bufferings and lags on high speed connection

[filippo_bistaffa]

In the last month I’ve experiencing some serious buffering problems, both with movie and music playback.
I am connected through a 300 Mbps connection and the server is connected through a 1 Gbps connection.
I can normally achieve a transfer rate of 20-30 Megabyte/s with SCP, so connection speed is not an issue.
Indeed, I could easily stream 1080p movies in original quality without any issue up until a month ago.

Now, it sometimes happen that Plex cannot even sustain FLAC playback (it buffers during a song).
This seems ridiculous to me, as SCP can transfer the entire song in a couple of seconds.
It can also happen that it takes 20-30 seconds to change to the next song.
Streaming movies with their original quality is now impossible, and I have to convert them to maximum 720p 4Mbps quality.
Again, this seems ridiculous as the connection could theoretically sustain a much, much higher bitrate.

Server Version#: 1.15.4.993

Other elements:

1. I use Plex via app.plex.tv with Chromium 73, but the same issues happen with Firefox, as well as with the Plex plugin on Kodi (on a Raspberry)
2. On the other hand, I can use Plex on my mobile (using mobile network) without issues, even though I only use it to stream transcoded music with reduced bitrate. Still, I never observed the 30-seconds-to-change-song problem.
3. Since it seems to be a network-related thing, I investigated a bit and noticed that, sometimes, there is actually a quite high packet loss rate when pinging the server (~20%, both from my home and from the mobile, probably due to congestion on the server’s network). Although a bit suspicious, this does not affect transfers with, e.g., SCP. Also, this was probably happening even when Plex was working perfectly a month ago, but I don’t have direct proof of this.
4. When issues happen, I sometimes notice that “remote access” gets randomly disabled (red ! icon), but it goes back to normal after a couple of seconds. Probably related to this, I sometimes noticed that Plex is connected in “indirect” mode, but, again, it goes back to normal after a couple of seconds.
5. I don’t see anything wrong in the logs (attached), although I see some “NAT: PMP, timed out waiting for response.” warnings.Plex Media Server Logs_2019-04-30_23-26-25.zip (496.8 KB)

[ChuckPa]

You pruned your logs so I can’t see any past activity.
What you show here is nothing failing.
If it’s buffering, it’s all LAN / external network related because there aren’t even any disconnects.

I do strongly suggest. Turn off IPv6 in Settings - Server - Network. Everything you have and access is IPv4.

[filippo_bistaffa]

I pruned previous logs to have a more concise thing to upload here, since the problem was also happening while these logs were being recorded.

[ChuckPa]

I could not see any errors in your logs. The buffering must be either network or CPU related since neither of those report in the logs in realtime.

[filippo_bistaffa]

The strange thing is that, for instance, I can mount my remote library folder via sshfs and play any file without any problem (with VLC for instance), no buffering of any kind nor lag when changing songs, etc.

[ChuckPa]

VLC renders on your computer directly on the glass with different codecs.
It reads the raw file and decodes locally.

Plex reads the file, decodes, and transmits the individual video frames.
A block read of the file might result in 30-40 seconds of video being rendered.
Sending 30-40 seconds of video frames is a lot of data given (1920x1080 pixels)

There is also a lot of handshaking required. Your round-trip time is not known.

The architecture is different. VLC is a ‘Thick Client’ (has its own codecs onboard). Plex/Web has no codecs. It’s a “Thin Client”. As said, every video frame must be sent.

Are Jumbo frames being used?
Anything else which induces network latency will cause this too.

The only thing I see are attempts to play in your logs. I see no active playing.

You also should consider turning off IPv6 (Settings - Server - Network) … You use IPv4.
It’ll just muck it up since PMS doesn’t fully support v6 yet.

To quantify the network, please have iperf3 installed and run it against from client and from server. This will definitive prove or disprove the networking component’s throughput.