It has been deleted. Check your bin to be sure.

You don't have permission to view it. Ask an admin to check your permissions allow you to see the folder that the asset is in.

You have a filter applied. Look in the left-hand side filters panel. If you have filters applied, they may be excluding the asset from the search. Try clearing the filters.

Try a different sort order. If you are looking for recently uploaded assets, for example, make sure to choose that as the sort order.

It is awaiting approval. If the uploader requires their uploads to be approved, the asset might not yet be approved yet. Check the approvals area.

It hasn't been fully uploaded yet. Users need to click "Done" in the upload screen to submit their assets into Dash. Try and upload a new file and see if the upload screen contains the missing assets.