Why are my whatsapp photos being overwritten?

[AC Question]

I have quite a lot of whatsapp photos on my S4, and I'm not sure if it is a bug or what, but I realized that for certain months (April, May etc), there are some photos which are duplicated. The original photo and the duplicated photo is exactly 10 days apart, and I'm pretty sure the two photos are different, I have no idea why one of them is being overwritten by the other, hence I end up having 2 copies of the same photo, when it's supposed to be 2 different photos (1 copy each).

Can anyone please help me? I treasure my photos a lot and I don't know what went wrong. Many thanks for any help given