  We present a comprehensive study of vortex matter and pinning evolution in
the FeSe$_{1-x}$S$_x$ system with various doping degree. The influence of
sulphur substitution on vortex pinning and peak effect occurrence is studied.
We show that there is a complex interplay among various pinning contributions
in the FeSe$_{1-x}$S$_x$ system. Additionally, we study a possible vortex
liquid-vortex glass/lattice transition and find an evidence that the vortex
liquid-vortex glass phase transition in FeSe has a quasi two-dimensional
nature. We investigate the upper critical field behaviour in FeSe$_{1-x}$S$_x$
system, and found that the upper critical field is higher than that predicted
by the Werthamer-Helfand-Hohenberg (WHH) model, whereas its temperature
dependence could be fitted within a two-band framework. Finally, a detailed H-T
phase diagram is presented.
