How to diagnose buffering on Plex

Ok I'm back:

It's not affecting the perf, it's still long to buffer...
Here some parts of the logs (still displayed on screen but not in a file...)

2019/04/04 23:17:41 DEBUG : Using config file from "/root/.config/rclone/rclone.conf"
2019/04/04 23:17:42 DEBUG : pacer: Rate limited, sleeping for 1.427277607s (1 consecutive low level retries)
2019/04/04 23:17:42 DEBUG : pacer: low level retry 1/10 (error googleapi: Error 403: Rate Limit Exceeded, rateLimitExceeded)
2019/04/04 23:17:42 DEBUG : pacer: Rate limited, sleeping for 2.647492788s (2 consecutive low level retries)
2019/04/04 23:17:42 DEBUG : pacer: low level retry 2/10 (error googleapi: Error 403: Rate Limit Exceeded, rateLimitExceeded)
2019/04/04 23:17:44 DEBUG : pacer: Rate limited, sleeping for 4.652301671s (3 consecutive low level retries)
2019/04/04 23:17:44 DEBUG : pacer: low level retry 3/10 (error googleapi: Error 403: Rate Limit Exceeded, rateLimitExceeded)
2019/04/04 23:17:46 DEBUG : pacer: Resetting sleep to minimum 100ms on success
2019/04/04 23:17:46 DEBUG : Google drive root 'Media_Center': Mounting on "/mnt/drive"
2019/04/04 23:17:46 ERROR : -o/--option not supported with this FUSE backend
2019/04/04 23:17:46 ERROR : --fuse-flag not supported with this FUSE backend
2019/04/04 23:17:51 DEBUG : vfs cache root is "/root/.cache/rclone/vfs/gdrive/Media_Center"
2019/04/04 23:17:51 DEBUG : Adding path "vfs/forget" to remote control registry
2019/04/04 23:17:51 DEBUG : Adding path "vfs/refresh" to remote control registry
2019/04/04 23:17:51 DEBUG : Adding path "vfs/poll-interval" to remote control registry
2019/04/04 23:17:51 DEBUG : : Root:
2019/04/04 23:17:51 DEBUG : : >Root: node=/, err=

2019/04/04 23:20:37 DEBUG : &{Radarr/BlacKkKlansman (2018)/BlacKkKlansman 2018.mkv (r)}: >Read: read=131072, err=
2019/04/04 23:20:37 DEBUG : &{Radarr/BlacKkKlansman (2018)/BlacKkKlansman 2018.mkv (r)}: Read: len=131072, offset=208207872
2019/04/04 23:20:37 DEBUG : &{Radarr/BlacKkKlansman (2018)/BlacKkKlansman 2018.mkv (r)}: >Read: read=131072, err=
2019/04/04 23:20:37 DEBUG : &{Radarr/BlacKkKlansman (2018)/BlacKkKlansman 2018.mkv (r)}: Read: len=131072, offset=208338944
2019/04/04 23:20:37 DEBUG : &{Radarr/BlacKkKlansman (2018)/BlacKkKlansman 2018.mkv (r)}: