Smart power switch works fine on a bench but fails to disengage the intended load on location
"It wouldn't disengage the load with both inputs floating"  

The offset drain current should be &lt;5uA.  Assuming there are no shorts or semi-conductive paths, (given the 12V supply) the only way the BTS117 could be conducting is if it damaged.

The input rather ESD sensitive w/only 3k volts of protection.  I'd recommended replacing it.