Hard to explain but let's say you selected an object. You go into parts menu and have a list of (select search, let's say inlets) and you have another piece highlighted (let's say strut). After hiding and showing all objects, that highlighted strut won't appear back even when searching up strut and trying to get it to show. And you can't find it under inlets because well, it's not an inlet so it disappears until you put hide all and show all again without the part selected
the missing strut is that pie cut slice in the middle
@Pedro by pressing the eye icon but that doesn't work