Question Gallery Hidden items lost!

Hi, one of my friend has an Galaxy S4

he had some photos and videos hidden in the gallery and today, he was trying to hide some new ones which didn't show the hide option
so, we cleared the cache and data of GALLERY from the Application manager
since then, we've been unable to find those hidden items
Can anyone tell what happened to them?

(however, we discovered that files photos/videos that are on SD card don't show HIDE option in the stock gallery)

but lost those hidden items that we hid earlier
anyone has any idea where they'd be? Changed Location or gone?
Thanks

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