Key Not Appearing in Game

[Mudbill]

The small chest's collision box is kinda lacking. If you place a key in there, it falls through the bottom of it (visually). When you hover your crosshair over it, it still glows blue around as normal, but you can see this through the mesh of the chest, therefore making it seem like the key is invisible.

If you do run into maps not updating your level editor progress, it could also be caused by a .map_cache file next to your .map. If that happens, delete it.