LTC2954 - powering down inadvertently

We have a LTC2954 as a switch for a device mounted in a vehicle, but not attached to power.  Its powered by lithium batteries.  On occasion, it seems that the switch is disabling power, yet the kill line is not asserted by the microprocessor, and it doesn't detect the external button being held down.

Other than the kill line or a long hold, what other situations could cause the EN to disable?  We added a capacitor to the kill line, but the random situation still seems to happen.

The documentation says that the PB line can withstand a static shock, but would a shock also cause EN to disable?

S1 is replaced with a polyfuse.