When content is stuck in the processing state for an unusually long time, it is indication that the content failed to upload the asset file. While in the Hub, you can see that the asset file is missing in the content editor accessed by the gear icon when hovering over the content in the All Media section.
The missing asset indicates a failure to upload content which is caused by a poor internet connection, corrupt file, not uploading from a local directory, or closing the upload page before 100% completion. Now that you've confirmed the asset file is missing, exit the editor by clicking Cancel at the top-right. Then, hit "Cancel" on the content that stuck processing to remove it entirely.
Finally re-upload the content using a stable internet connection, a file from a local directory, and wait to see the upload completed to 100% before exiting the page.
