LT3845 SHDN pin behaviour
Typically you want to have some hysteresis in your shutdown thresholds so it is not constantly oscillating between on and off states.

Usually switching the load off of real world power sources will have the voltage recover a bit, thus you would immediately switch on again, just to drop the voltage because it is being loaded.

To mitigate this problem you want the switch on to be quite a bit higher than the switch off so that you have a decent chance of preventing this oscillation and your circuit being off even when the load is gone.