Exotic conditions for the existence and evolution of nonlinear spin ensembles (domain walls, spin solitons, skyrmions) in molecular-based magnets are incarnated in the macroscopic response of magnetization corresponding to collective stochastic behavior. The molecular ferrimagnet ${\mathrm{K}}_{0.4}[\mathrm{Cr}{(\mathrm{CN})}_{6}][\mathrm{Mn}(\mathrm{R}/\mathrm{S})\ensuremath{-}\mathrm{pn}](\mathrm{R}/\mathrm{S})\ensuremath{-}\mathrm{pn}{\mathrm{H}}_{0.6}$ manifests three types of magnetic relaxation: (a) continuous decay of magnetic moment, (b) stepwise relaxation by stochastic magnetization jumps, and (c) a single jump of magnetization in threshold magnetic field. Continuous relaxation at 20--50 K is provided by domain wall movement described in the frames of a strong pinning model, while a low-temperature continuous component of relaxation does not follow this model. Stepwise stochastic relaxation was observed below 8 K in both a sweeping reverse magnetic field and a stationary reverse magnetic field. Statistical treatment of the postponed magnetization jumps revealed a multimodal amplitude distribution of stochastic magnetization jumps corresponding to magnetic moment transitions between few clear distinguishable levels. Spectral density of magnetization jumps in a stationary magnetic field corresponds to white noise, while spectral density in a sweeping magnetic field manifests pink noise $\ensuremath{\sim}1/f$ provided by self-organized criticality. Postponed emission of magnetic noise in the ${10}^{\ensuremath{-}6}\ensuremath{-}5\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}1}\phantom{\rule{0.16em}{0ex}}\mathrm{Hz}$ frequency range was observed in stationary conditions in contrast to Barkhausen noise.