External subtitles

Hi guys. I'm new with Serviio (used to use PS3 Media Server and Plex) and I'm trying to play an MKV movie with external subtitle(.srt) but I can't make it work.
In subtitle page, I checked "use subtitles" but without sucess. The only way that I can make it work is using option "Enable Burn-in Subtitles" but when I use it, video streaming is is flattened and a lot of parts of subtitle is skipped.

I'm already tried:
-format utf-8
-SRTWiz to fix subtitle
-name is the same from MKV file

Thanks for any help.