I'm seeing almost constant stuttering and freezing on the latest version of the XBOX One PLex client.. when it happens I see this in the log:
Jan 01, 2016 17:35:51 [0x10b681000] ERROR - handle_stream_read error 54 Connection reset by peer
Jan 01, 2016 17:35:51 [0x10b681000] WARN - LongPoll: Got error, closing.
Jan 01, 2016 17:37:19 [0x10b681000] ERROR - handle_stream_read error 54 Connection reset by peer
Jan 01, 2016 17:37:19 [0x10b681000] WARN - LongPoll: Got error, closing.
Jan 01, 2016 17:38:47 [0x10b681000] ERROR - handle_stream_read error 54 Connection reset by peer
Jan 01, 2016 17:38:47 [0x10b681000] WARN - LongPoll: Got error, closing.
Jan 01, 2016 17:40:15 [0x10b49c000] ERROR - handle_stream_read error 54 Connection reset by peer
Jan 01, 2016 17:40:15 [0x10b49c000] WARN - LongPoll: Got error, closing.
Jan 01, 2016 17:41:44 [0x10b681000] ERROR - handle_stream_read error 54 Connection reset by peer
Jan 01, 2016 17:41:44 [0x10b681000] WARN - LongPoll: Got error, closing.
Jan 01, 2016 17:43:12 [0x10b681000] ERROR - handle_stream_read error 54 Connection reset by peer
Jan 01, 2016 17:43:12 [0x10b681000] WARN - LongPoll: Got error, closing.
Jan 01, 2016 17:44:40 [0x10b49c000] ERROR - handle_stream_read error 54 Connection reset by peer
Jan 01, 2016 17:44:40 [0x10b49c000] WARN - LongPoll: Got error, closing.
.. sometimes the app actually freezes during playback. This can take anywhere between 7 seconds to 2 minutes to resolve itself.
I'm about 80% confident that this only occurs on .MKV files. All appear to have AAC encoding, as well (same confidence). Content bandwidth doesn't appear to be the issue: This happens at 1080p, and 720p also.
The Plex Server is a pimped Mac Mini i5 2.5GHz w/ 16GB RAM, and TOTAL CPU never really exceeds 15-20% ... running 1GBE to the XBOne (ie. NOT WiFi). There should be no network or server CPU constraints affecting this issue.
I don't see a lot of matches for this LongPoll issue in the Plex Forums.. this could be an interesting one.