Having similar issues with a FreeBSD server instance; local devices have given up syncing, and are unable to sync.
Server was reporting most of the devices not having connected in a significant period of time (devices IDs reset somehow?), so wiped out all the devices, and tried to reconnect & resync a Nexus 7 to no luck.
Server version 1.7.3.3937
Here’s a dump from the server (usernames & IPs pruned somewhat; verbose attached as a text file) after attempting to reinitiate the sync operation on a small (limited to 2 episodes) TV sync:
Jun 24, 2017 22:30:59.828 [0x80a27ad00] DEBUG - Auth: We found auth token (xxxxxxxxxxxxxxxxxxxx), enabling token-based authentication.
Jun 24, 2017 22:30:59.828 [0x80a27ad00] DEBUG - Auth: authenticated user 9747497 as <syncing_user>
Jun 24, 2017 22:30:59.828 [0x80b04f400] DEBUG - Request: [home.ip.network.86:35275 (WAN)] GET /sync/668d5f7e62b5e3b2-com-plexapp-android/status (6 live) TLS GZIP Signed-in Token (<syncing_user>)
Jun 24, 2017 22:30:59.834 [0x80a27a800] DEBUG - Completed: [home.ip.network.86:35275] 200 GET /sync/668d5f7e62b5e3b2-com-plexapp-android/status (6 live) TLS GZIP 5ms 906 bytes (pipelined
: 7)
Jun 24, 2017 22:31:01.139 [0x80a27a800] DEBUG - handleStreamRead code 335544539: short read
%2Cplayback%2Cnavigation%2Cmirror%2Cplayqueues&timeout=1&X-Plex-Product=Plex%20Web&X-Plex-Version=3.7.0&X-Plex-Client-Identifier=51yeh7usj9oc51dc547pmbzw&X-Plex-Platform=Safari&X-P
lex-Platform-Version=10.1&X-Plex-Device=OSX&X-Plex-Device-Name=Plex%20Web%20%28Safari%29&X-Plex-Device-Screen-Resolution=1159x748%2C1680x1050&X-Plex-Token=xxxxxxxxxxxxxxxxxxxx
Jun 24, 2017 22:31:01.174 [0x80a27ad00] DEBUG - Auth: We found auth token (xxxxxxxxxxxxxxxxxxxx), enabling token-based authentication.
Jun 24, 2017 22:31:01.174 [0x80a27ad00] DEBUG - Auth: authenticated user 1 as <admin_user>
Jun 24, 2017 22:31:01.174 [0x80a27a800] DEBUG - Auth: We found auth token (xxxxxxxxxxxxxxxxxxxx), enabling token-based authentication.
Jun 24, 2017 22:31:01.174 [0x80a27ad00] DEBUG - Auth: Came in with a super-token, authorization succeeded.
Jun 24, 2017 22:31:01.174 [0x80a27a800] DEBUG - Auth: authenticated user 1 as <admin_user>
Jun 24, 2017 22:31:01.174 [0x80a27a800] DEBUG - Auth: Came in with a super-token, authorization succeeded.
Jun 24, 2017 22:31:01.174 [0x80b04f400] DEBUG - Request: [home.ip.network.97:53940 (WAN)] GET /player/proxy/poll?deviceClass=pc&protocolVersion=1&protocolCapabilities=timeline%2Cplayback%2Cnavigation%2Cmirror%2Cplayqueues&timeout=1 (7 live) TLS GZIP Signed-in Token (<admin_user>)
Jun 24, 2017 22:31:01.175 [0x809af1600] DEBUG - Request: [home.ip.network.97:53939 (WAN)] GET /sync/transcodeQueue (7 live) TLS GZIP Signed-in Token (<admin_user>)
Jun 24, 2017 22:31:01.177 [0x80b04f400] DEBUG - Beginning read from two-way stream.
Jun 24, 2017 22:31:01.179 [0x80a27a800] DEBUG - Completed: [home.ip.network.97:53939] 200 GET /sync/transcodeQueue (7 live) TLS GZIP 4ms 470 bytes (pipelined: 1)
Jun 24, 2017 22:31:04.793 [0x80a27a800] DEBUG - Auth: We found auth token (xxxxxxxxxxxxxxxxxxxx), enabling token-based authentication.
Jun 24, 2017 22:31:04.793 [0x80a27a800] DEBUG - Auth: authenticated user 1 as <admin_user>
Jun 24, 2017 22:31:04.793 [0x80a27a800] DEBUG - Auth: Came in with a super-token, authorization succeeded.
Jun 24, 2017 22:31:04.794 [0x80c643500] DEBUG - Request: [home.ip.network.126:35284 (WAN)] GET /status/sessions (8 live) TLS Signed-in Token (<admin_user>)
Jun 24, 2017 22:31:04.794 [0x80c643500] DEBUG - [Now] Adding 0 sessions.
Jun 24, 2017 22:31:04.795 [0x80a27ad00] DEBUG - Completed: [home.ip.network.126:35284] 200 GET /status/sessions (8 live) TLS 1ms 292 bytes (pipelined: 1)
Jun 24, 2017 22:31:19.808 [0x80a702e00] DEBUG - NetworkInterface: PF_ROUTE socket received message. Version 5, Type 0x6, Len 200.
Jun 24, 2017 22:31:21.193 [0x80a27ad00] DEBUG - handleStreamRead code 335544539: short read
%2Cplayback%2Cnavigation%2Cmirror%2Cplayqueues&timeout=1&X-Plex-Product=Plex%20Web&X-Plex-Version=3.7.0&X-Plex-Client-Identifier=51yeh7usj9oc51dc547pmbzw&X-Plex-Platform=Safari&X-P
lex-Platform-Version=10.1&X-Plex-Device=OSX&X-Plex-Device-Name=Plex%20Web%20%28Safari%29&X-Plex-Device-Screen-Resolution=1159x748%2C1680x1050&X-Plex-Token=xxxxxxxxxxxxxxxxxxxx