Why is my Chromecast buffering ?




I'm having an issue with my chromecast.
It was working fine before I change my modem and almost at the same time, the open media vault (2->3) where PMS is installed.

Since, when I play a MKV, it freeze, sometimes every 5 minutes, sometimes never on a 40min tv show ...
Even with the file with low quality (4mbps), or higher (10/12Mbps).

I saw on the log that plex always transcode file for the chromecast, and that message :
[Chromecast] Player: Excessive buffering detected; network

On the file below, I just restart PMS, then play a file, and it freeze at 18h30 (first second of playing), then around 18h36.

Can you help me ?