Another good app to help track down space usage is DiskUsage:
https://play.google.com/store/apps/details?id=com.google.android.diskusage&hl=en
It showed me that the Downloader system app was using 1.5GB of cache on my Note 4.
That's a very handy app to find where you can quickly figure out what is taking a lot of space and delete it on the spot.
Thanks for sharing!
Maybe check thumbdata files/folders in the DCIM folder of device storage. Same thing happened to me a couple of years ago on a Samsung Tab 2 7.0 and those files were the culprit.
Yep, that's a great app. Been using it on all my devices for a couple of years.This was another case where the DiskUsage app showed me large usage - thumbnails:
https://play.google.com/store/apps/details?id=com.google.android.diskusage&hl=en