When you don't receive a photo what is the usual cause?

Hello,

Pretty broad title but I am wondering what is the reason some photos do not send? For instance, I have my camera on photo + video, when I look at the numbers on the photo the photos are even or odd numbers and the videos I request are the opposite. I will show a photo but I received photo 20, and 24 but not 22. This seems to happen far too often. When I pull the SD cards after changing batteries I notice that I am looking at photos that were never sent. This happens frequently, and I understand if it happens when the batteries are low. But I just put brand new batteries in my camera and went to go look at my camera after it missed a photo and to my surprise here is the buck I am after.

Thanks