I see nothing obviously ‘wrong’ in Outliner in this model.
But I have a few comments.
You can most easily see every individual component or group in Outliner by clicking the broad arrow top right, and selecting Expand all
When I do that, I see this (in part):
You have at least two double-nested groups that don’t need to have the second level of nesting - the Plywood group has another group inside it also called Plywood; and the shoe-rack top (called just Group) does the same.
It isn’t a requirement, but it is generally a good idea to give meaningful names to Components as you create them, not just leave them with the default name Component#1, …#2, etc.
And I would almost never use Groups rather than components. If you do, use Entity Info to give them meaningful Instance names, but don’t use Groups if you have numerous identical elements in the model. If you edit one copy of a component, all the others change to match, which is usually useful.
If you want one or more components to differ from the others like them, select one or more, then R-click and Make Unique. Those will all become different components from the original, but all be identical to each other.
For example, your Shoe rack is all loose geometry inside one large component. I would have made a component of one individual shoe pocket, then copy it to all the others (except the bottom one, which seems not to have partitions). You could probably also make the bottom one by Scaling one of the narrow ones by four times along the red axis.
And your shelving at the back has a reversed face, several missing faces, and some unneeded central lines.
The shelving could also be made of components - one component for the top, the bottom, and the middle shelf; then a separate one for all the vertical partitions - they look all the same.
If you still have the problem in Outliner that you originally posted about, in the full model, try uploading it to Dropbox or a similar file sharing service, and share a link here.
Thanks for completing your profile. It’s helpful.