The highest reported efficiencies of metal halide perovskite (MHP) solar cells are all based on mixed perovskites, such as (FA,MA,Cs)Pb(I1-xBrx)3. Despite demonstrated structural changes induced by light soaking, it is unclear how the charge carrier dynamics are affected across this entire material family. Here, various (FA,MA,Cs)Pb(I1-xBrx)3 perovskite films are light-soaked in nitrogen, and changes in optoelectronic properties are investigated through time-resolved microwave conductivity (TRMC) and optical and structural techniques. To fit the TRMC decay kinetics obtained for pristine (FA,MA,Cs)Pb(I1-xBrx)3 for various excitation densities, additional shallow states have to be included, which are not required for describing TRMC traces of single-cation MHPs. These shallow states can, independently of x, be removed by light soaking, which leads to a reduction in the imbalance between the diffusional motion of electrons and holes. We interpret the shallow states as a result of initially well-intermixed halide distributions, which upon light soaking segregate into domains with distinct band gaps.