Measurements of branching fractions of ${\mathrm{\Lambda }}_c^{+}\to {\mathrm{\Sigma }}^0{K}_S^0{\pi }^{+}$ and ${\mathrm{\Lambda }}_c^{+}\to {\mathrm{\Sigma }}^0{K}_S^0{K}^{+}$

Based on a data sample corresponding to an integrated luminosity of 6.4~fb${}^{-1}$ of $e^{+}{e}^{-}$ annihilation and collected with the BESIII detector at 13 center-of-mass energy points ranging between 4.600~GeV and 4.950~GeV, we report the first observation of the singly Cabibbo-suppressed decay ${\mathrm{\Lambda }}_c^{+}\to {\mathrm{\Sigma }}^0{K}_S^0{\pi }^{+}$ with a statistical significance of 5.9$\sigma$. The branching fraction is determined to be $\mathcal{B}({\mathrm{\Lambda }}_c^{+}\to {\mathrm{\Sigma }}^0{K}_S^0{\pi }^{+})=(0.58\pm {0.14}_{\mathrm{s}\mathrm{t}\mathrm{a}\mathrm{t}\mathrm{.}}\pm {0.04}_{\mathrm{s}\mathrm{y}\mathrm{s}\mathrm{t}\mathrm{.}})\times {10}^{-3}$. In addition, the decay ${\mathrm{\Lambda }}_c^{+}\to {\mathrm{\Sigma }}^0{K}_S^0{K}^{+}$ has also been investigated, and the first evidence for this decay is obtained with a statistical significance of 3.7$\sigma$.