You likely downloaded a "topology icon" version. Search for "Zyxel front elevation visio" or look for stencils labeled "Detailed" or "Front/Rear."
Accurate dimensions ensure that your rack diagrams reflect real-world constraints. Zyxel Visio Stencils
Zyxel often reuses chassis designs. Use a stencil from a similar-sized device (e.g., use a USG FLEX 50 stencil for a new ATP 100) and manually add text labels. You likely downloaded a "topology icon" version