Question VOD not playing from middle

[whiteiptv]

I hope someone has already faced this problem and know what it is about
VOD are installed on the server ,well encoded by Xtream UI .
when I click on a VOD to play it plays well and fast
but if I want to move forward , resume , play from middle .... hangs , cannot
did I miss some settings to add ? some encoding ? movies are mkv format
thank you

 

[jacob1980]

check sources files and also check encoding