Comment on "On the general relativistic framework of the Sagnac effect" EPJC 79:187

In a recent paper EPJC 79:187 the general relativistic framework of the Sagnac effect was investigated. We have some comments on this paper. We show that their conclusion about the apparent variation of the speed of light does not hold in stationary spacetimes. Also, We show that their definition of gravitational Coriolis potential and gravitational Coriolis time dilation are inconsistent with what is stated in standard references.