If you place small objects on the 'Spartan' monument on the south coast of Stratis, they fall through it, which can make them impossible to see. The clipping seems off.

I tried with the launchers ammo box and with a backpack.

The launchers would fall half-through if dropped from 0.5m, or be completely invisible if placed at ground level. The backpack fell right through even from 0.5m.