Photos incorrectly showing as assigned to Album

I deleted all my Albums as I want to start organizing my photos from scratch. I created a Smart Album to confirm that all photos are indeed unassigned from Albums ("Album...is...Any"), and this album shows a few hundred photos. This shouldn't be as I have zero Albums. Looking at the photos in the Smart Album, it looks like these were previously assigned to Albums that I recently deleted. Some of them I deleted today, although several hours ago. I have shut down and restarted my computer but the issue persists. Does anyone know why this is happening?