This is a bug that needs to be reported to the support service via the form at the link: Submit a bug report.
You also wrote about it here: Delete all button to remove all the files at once
And so that you can select and delete all files right now, you need to start dragging the mouse a little to the left of the files thumbnail or a little to the right of the “Restore file” buttons. In your screenshot, these places are behind the selection.