if you lower the speed of the audio clip, it will also lower the pitch, BUT it will be a different duration (longer),
so maybe that’s what made your clip go out of sync?
adding the Pitch Audio Filter should not affect sync
(actually i’ve seen it slip the sync by a frame on export)
this filter CAN NOT be scrubbed, so when it’s applied, if you try to scrub the audio, it will appear to be silent
it can only be played in real time.
a tip for this filter:
it takes a few frames to settle in. the first few frames will sound scratchy and crackly,
so trim the clip back 12 frames, say, or a second,
and volume graph that extension down.
nick