After uploading one or more documents, it is normal that they are not displayed immediately.
In the upper right corner you can get an overview of the upload status per document via the notification icon. When all documents have been uploaded, click the refresh button next to the upload button. The overview will be updated, after which your documents will be visible.
Also, be sure to sort the documents by the “ModifiedOn” column so that the most recently modified documents are displayed at the top.
Check the active filters, there may be some filters active that do not match the metadata of the documents you just added.