Subtitle disseapears after 20-30 minutes of playback

I noticed one strange thing after last plex media server update : in chromecast playback, the subtitle just dissapears after 25-30 minutes. The movie continue to play but no subtitles. If i stop de movie and replay from where it was, the subtitle reappears ...but disseapears again 20 minutes later.
It happens only on chromecast, did not noticed the same problem on web or samsung tv....