We uncover a symmetry-filtered mechanism for anomalous dissipative relaxation in a long-range XXZ spin chain subject to local dephasing. At the isotropic point, the coherent Hamiltonian has global symmetry, whereas the full Liouvillian retains only the symmetry associated with total magnetization. This structure pins a family of spatially uniform zero--charge left eigenoperators with exact eigenvalues , forming a Liouvillian relaxation comb. For the ferromagnetic Dicke ground state, the overlap envelope on this comb is known exactly at finite size and becomes Gaussian in the large- limit. Since higher- components decay rapidly, the comb tooth controls the long-time dynamics and yields universal relaxation independent of system size and interaction range. This mode-accessibility filtering realizes a spectral strong quantum Mpemba effect: an initially farther state relaxes faster than closer thermal states because slow non-steady Liouvillian modes are inaccessible. Weak breaking of the Hamiltonian symmetry restores slow-mode overlap and suppresses this acceleration.