When dropping gear, ILS should pop up. This is not the case sometimes. It's either using it for another airport/airstrip or not showing up at all. I had several times where I tried to land on Altis, either Molos Airfield, Athira Airport, Airfield near Krya nera, or AAC airfield on Altis.
I get it sometimes, and usually get it after take-off from one of these airfields, however not always when landing (Gear and Flaps down).
I can answer this real quickly for you this isn't a bug but this is more of how Landing strips are made. AI program to land in one direction of the Airfield and take off in another never the opposite. with this the ilS only shows when you're coming in from The Landing side of the Airfield not the takeoff. in conclusion runaways are like a one-way Street and the ILS will not show up unless you were coming and in their correct direction. hope this helped