It is not uncommon to have a time step fail to converge or even diverge. This is sometimes caught by field variables reporting unphysical values (negative volume fraction, negative pressure, negative density, etc.) In the even that this happens, the adaptive time stepping algorithm in MFIX will decrease the time step size (dt) and restart the time step. Usually the code can recover from these events.
The Outflow BC defined: IJK_P_g remaining undefined is a normal message. It means that the MFIX has detected a pressure outflow and will not impose any constraints on the pressure field. If no outflow is given, MFIX will fix the pressure in a single cell to improve convergence and prevent the pressure field from wondering.