I've installed a few of these and I think what is happening with yours is the unit is too close to the cabinet on the hinge side. The only way to fix it right is to take out the mounting screws that hold the refrigerator in the cabinet then move the refer over about a 1/8 to 3/16th inch to allow room for the finger guard to slide freely. This is something the installer should have been checking for before putting in the mounting screws.

My installers didn't put in the finger guard, and since I don't have little ones anymore, I didn't call them on it. Do you think there's an issue for older kids and adults?

It's a big door door and the way the hinge operates there is a certain shearing action on the hinge side.
Because I have a major and justified fear of being sued I would never install product without also installing all the safety devices recommended by the manufacturer.
You may only have older children or adults in the household but does that mean you never entertain visitors who may have small children? Will you ever move? Will a family with small children move in? As you can see there are way too many varibles in life which is why I lean to the side of being over cautious rather than under.

I need a replacement finger guard. Where can I find one?

i am also looking for the same thing