images and videos cannot be displayed over time

[Arno Tromp]

When I make photos with my Nokia Lumia RM978 the images are stored in my 'Photos' folder, visible at first, but after a while the image pictograms are shown blank and when I pick one to see full size it doesn't show up, instead i get the message: cannot load the photo, try again later. But it never shows up again, not in months! The same with videos (message: this fil cannot be played on your phone).
I have the stuff stored on a 128 GB mini SD card, it seems to work well, only 15 GB is used, but could this card anyhow be the problem??