When the canoe drops from the ceiling and starts to plummet towards Lindsay Pagano, she is standing in front of the stage. But when Fred pushes her out of the way a moment later, she is now on the stage.
When Lindsay Pagano is rehearsing, there is a moment where she walks across the stage and the camera pans up to the screen above her head. Then Lindsay on the screen is clearly standing still. At the same time, Velma's arms abruptly move from her hips to behind her back.
After Shaggy helped Fred out of the magic cabinet, the latter's eyebrow colors change blonde, and stayed when he unmasked the ghost, and changed back to black in the next scene.