We examine the influence of various dissipative mechanisms on the transport properties of molecular polaritons in a FP cavity using the mean-field Ehrenfest (MFE) quantum dynamics method to simulate the dynamics of the hybrid light-matter system. Notably, polariton transport occurs in a collective regime in which a substantial number of excitons (thousands or more) are resonantly coupled to cavity modes, resulting in upper polariton (UP) and lower polariton (LP) bands, as well as dark states that do not contain any significant photonic character. To faithfully model the transport process, one needs to consider at least N = 10 4 -10 6 molecules and M = 10 2 -10 4 cavity modes (that satisfy the dispersion relation), presenting a significant computational challenge. Existing theoretical work either does not consider cavity loss or is limited to the size of the system 7 in the transport simulations (such as only using N = 512 molecules and M = 160 modes in Ref.