Comment on “Modulational instability and frequency combs in whispering-gallery-mode microresonators with backscattering”

Some years ago, to investigate modulational instability using a linear stability analysis, Kondratiev and Lobanov [Phys. Rev. A 101, 013816 (2020)] applied a method that consists of adding complex conjugate equations to a differential system to close up the system self-consistently. It is the aim of this Comment to note and correct the crucial inconsistency found in the method used to investigate the modulational instability in Kondratiev and Lobanov's work.