Hard to say what the issue is, the game certainly is a bit more gpu demanding that other submissions here just by the nature of everything we're doing.
One thing to note with the audio/video sync we tried to limit ourselves to using the unity audio system, but this is actually a big hindrance to us, as it's not good for doing exact audio/video sync on most platforms and at best our current solution is a hack.
As for the pause feature, yes it's just a pause functionality we didn't have time to flesh out a pause menu for the jam release unfortunately. As for the game restarting after the end of the song we never hit this issue, it should go straight to the results screen. Perhaps there a bug triggered by lower performance on lower end machines causing issues.
In any case we're looking at doing some updates after the rating period is over to fix a lot of the issues with the initial release but that doesn't really help out with the jam version.
Thanks for the feedback!