@ncw I've been looking for and I think I've found the thread where I commented that I saw someone who was experiencing the same problem as me.
As I have understood in the last comments the problem should have already been solved, but I still happen (I use the last stable version 1.35).
Here, I believe, the problem is also mentioned, although it is not exactly the same ("Movie will often pause or "jump" ahead, sometimes the movie will just stop, sending you back to the Plex menu."): Plex server with Amazon drive - rclone crypt vs encFS speed - #5 by Stokkes
If someone can help me, I would appreciate it.
Sorry for my bad english, thank you very much!