Since it only happens with the grip safety engaged, wouldn't it more likely be the 'grip safety leg' that is the issue?
The grip safety leg just controls how much pressure it takes to depress the grip safety, it has nothing to do with the sear or disconnector. When the grip safety is unpressed, it physically blocks the back end of the trigger bow.
A combination of sear spring pressure and hammer spring pressure (the one in the base of the grip) is what holds the sear in contact with the hammer hook.