I'm on the FreeLipSync team. Our Cartoon Lip Sync page now shows two examples using the same character image: one spoken line and one singing clip. Keeping the image fixed makes it easier to focus on what changes with the audio.
For speech, listen for word timing and check whether the mouth settles naturally during pauses. For singing, pay particular attention to sustained vowels, the transition between notes, and whether the mouth stays active through a held syllable. These are review points, not a promise that every input will work equally well.