I'm having the same issue. Turns out that the Proxy render size under View Settings, Really destroys the accuracy of the video in preview.
Notice how the 'Text' and 'Character' deviates from its original location.
Images and Videos are not affected, But Text, Any sort of animation is affected.
The solution I found for myself is to fix all the glitches manually in full render settings.
Edit:
Turn on AV Sync. You will find it under Timeline-> Playback -> AV Sync (check mark).