When using the Double Cut feature as found in the Silhouette Cut Settings screen in the Silhouette Studio® program, the secondary cutting pass is not aligned with the initial cut made. There are not concerns with alignment when performing a single pass cut. The issue only presents itself when using the Double Cut feature.
The material is somehow slipping. Using the double-cut feature indicates a thicker material type is in use. As material thickness increases, the rollers (dependent upon the material type and surface) may not grip as firmly on the media's surface during operation. The resulting misalignment can thus either be the result of the roller slipping off material's surface OR a concern with the cutting mat not holding the material in place properly.
The following steps can be taken to explore and resolve the concern: