Lightroom -- store a copy of all originals not copying all photos (my backups are incomplete!)

Hi,

I've noticed my "local originals copy" file count was much lower than my cloud storage count. When I investigate I see that entire date ranges are missing in the local copy directory. However, if I browse to the "missing" photo in lightroom it then does appear in the folder after a short delay (I'm assuming to download).

Lightroom claims all of my photos are synced and up-to-date, but obviously something is wrong.

I've tried uninstalling lightroom and deleting the AppData directory to start fresh, with a re-download of all of my photos but the issue is still occuring.

How can I be sure all of my photos are being locally copied so I can keep a local backup?