I have almost the same issue, my lipsync has mouth sprite keys, audio and everything but it simply sometimes stopps working, is delayed by seconds or other stuff.

this is horrible

Hi all - I am adding a high-quality audio clip (mp3/wav file) to several morph-based characters, but the mouth hardly moves. Increasing the expressiveness slider on each mouth lip movement doesn't do much to improve this. Any help on how to automatically increase or exaggerate lip movement would be really appreciated! Thanks