In 2021 problems with quench protection system resulted in two accidents with superconducting (SC) magnets of the JINR Booster. Each accident resulted in extensive repairs. However, the recorded signals of voltage and current in the magnets enabled detailed analysis of quench development well beyond the safety margin. This text presents analytical and numerical analysis of the data presented in the Part I of this paper. First, the quench propagation speed, and changes with time in the conductor temperature distribution and the total resistance of the magnet string are considered. Then possible reasons of the discrepancy between measurements and simulations are discussed.