  Employing analytical methods and quantum transport simulations we investigate
the relaxation of quasiparticle spins in graphene proximitized by an $s$-wave
superconductor in the presence of resonant magnetic and spin-orbit active
impurities. Off resonance, the relaxation increases with decreasing temperature
when electrons scatter off magnetic impurities---the Hebel-Slichter
effect---and decreases when impurities have spin-orbit coupling. This distinct
temperature~dependence (not present in the normal state) uniquely discriminates
between the two scattering mechanisms. However, we show that the Hebel-Slichter
picture breaks down at resonances. The emergence of Yu-Shiba-Rusinov bound
states within the superconducting gap redistributes the spectral weight away
from magnetic resonances. The result is opposite to the Hebel-Slichter
expectation: the spin relaxation decreases with decreasing temperature. Our
findings hold for generic $s$-wave superconductors with resonant magnetic
impurities, but also, as we show, for resonant magnetic Josephson junctions.
