Samsung Galaxy S5 mini lost all photo and video

As the title says, the phone simply lost all photos and videos ever taken. It worked fine yesterday evening and photos and videos were taken, and then replayed an hour or so later. Yet now there are no photos or videos at all. Not from last evening, nor from before. I'm not the person using the phone, but apparently there was no notification or anything. Simply in the morning the pictures weren't there. The internal clock also reset itself, but all other apps, pictures and data are still in place and unchanged, so I don't think it could have been a factory reset. I'm also told that nothing was done on the phone that could have remotely cause this. All the pictures on the SD card which were put there manually are still there and accessible. Only the media in the DCIM folder (both on the phone's memory and the SD card) seems to have vanished entirely and without a trace. Most of the pictures weren't backed up anywhere (especially those taken the last few days or weeks, since others may or may not have been backed up somewhere), so I'm at a lost on how to proceed.

The android version is the stock version which came with the phone when it was new and the phone wasn't rooted. It didn't suffer any damage and aside from loosing the pictures is fully functional. I didn't try taking new pictures out of fear that I might overwrite old ones in the process, but the camera app loads normally and seems to work.

tl;dr: as the title says, a Samsung Galaxy S5 mini had all of the pictures and video taken by the stock camera app disappear without a trace overnight.

I'd appreciate any help on the matter.