Is there a reason why my simulation in Lumerical FDTD sometimes ends before it reaches 100%?

Two parameters determine the simulation time:

1-Simulation time is determined by meshing, geometry, material, and boundary conditions.

2- Auto shutoff min (Right click on FDTD —> Advanced option)

An auto shutoff level is displayed in the job manager window of FDTD when you run a simulation, which is a measure of how much energy is left in the simulation window. Based on this value, it can be determined whether or not the simulation can be stopped before the end of the simulation time.

Using 1e-5 as the default value for auto shutoff, we have two assumptions: first, if the energy is below this default value, the simulation will stop and this message will appear in the log file:

As you see in this picture the simulation is finished at 58%. By default, the program internally checks for autoshutoff conditions every 100 time steps of the simulation; however, this is only a very small fraction of the total simulation time, less than 1% of the entire simulation time, which is why the program internally checks for autoshutoff more frequently than it does in the job manager.