Conventional s-wave superconductivity and hidden peak effect in single crystals of Mo₈Ga₄1 superconductor

London and Campbell penetration depths were measured in single crystals of the endohedral gallide cluster superconductor, Mo₈Ga₄₁. The full temperature range superfluid density is consistent with the clean isotropic $s-$wave weak-coupling BCS theory without any signs of the second gap or strong coupling. The temperature dependence of the Campbell length is hysteretic between zero-field cooling (ZFC) and field-cooling (FC) protocols, indicating an anharmonic vortex pinning potential. The field dependence of the effective critical current density, jc(H), reveals an unusual result. While in the ZFC protocol, jc(H) is monotonically suppressed by the magnetic field, it exhibits a profound ``hidden'' peak effect in the FC protocol, that is, without a vortex density gradient. We suggest a possible novel mechanism for the formation of the peak effect, which involves both static and dynamic aspects.