VLC’s subtitle sync delay function not working as expected
Solution 1:
Have you tried the advance synchronization feature (if your subtitles are lagging behind the audio).
Press shift+H when you hear a line spoken, and shift+J when you see that line in the text. Or you can also use the delay time box in the Adjustments -> Synchronization window.
https://wiki.videolan.org/Adjust_Subtitle_Delay/