Scanning superconducting quantum interference device imaging of ${\mathrm{CaSb}}_2$ reveals dense vortex clusters with enhanced boundary susceptibility and suppressed internal vortex motion, features that are inconsistent with both isolated-vortex and flux tube behaviors. These measurements provide a local visualization of magnetic dynamics within vortex clusters in a weakly pinned superconductor, offering an alternative route to probe nonmonotonic vortex-vortex interactions that are typically expected in single-band type-II/1 or multiband type-1.5 superconductors. Although the superfluid density follows a single-gap BCS model, vortex clustering and spatially inhomogeneous dynamics are clearly observed in a regime where reported Ginzburg-Landau parameters place ${\mathrm{CaSb}}_2$ near the type-I/type-II boundary.

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• Multiband superconductivity
• Superfluid density
• Vortices in superconductors
• Scanning probe microscopy