  Nonlinearity and discreteness are two pivotal factors for an emergence of
discrete breather excitations in various media. We argue that these
requirements are met in the forced ferromagnetic phase of the monoaxial chiral
helimagnet CrNb$_3$S$_6$ due to specific domain structure of the compound. The
stationary, time-periodic breather modes appear as the discrete breather
lattice solutions whose period mismatches with a system size. Thanks to
easy-plane single-ion anisotropy intrinsic to CrNb$_3$S$_6$, these modes are of
the dark type with frequencies lying within the linear spin-wave band, close to
its bottom edge. They represent cnoidal states of magnetization, similar to the
well-known soliton lattice ground state, with differing but limited number of
embedded $2\pi$-kinks. Linear stability of these dark breather modes is
verified by means of the Floquet analysis. Their energy controlled by two
parameters, namely the breather lattice period and amplitude, falls off
linearly with a growth of the kink number. These results may pave a new path to
design spintronic resonators on the base of chiral helimagnets.
