There is a safety setting in the Propagate segment which prevents runaway propagation if Astrogator does not find a stopping condition.
If an Astrogator satellite only propagates for 100 days, and you want it to continue, click the Advanced... button next to the propagator name in the Astrogator MCS window. Change or disable the maximum propagation times. This parameter prevents STK Astrogator from propagating indefinitely in the case where the propagator does not detect any stopping conditions.
Also, the maximum propagation time for a finite maneuver is one day, which you may need to change for low thrust maneuvers.
See the STK Help for more information about the
Propagate segment properties.
