Same issue with me, I am using Samsung Galaxy Note 3, running Android 5.0 (not root).
The photos are saved the External SD Card (not internal memory), the SD Card is a SanDisk Ultra 64GB MicroSD XC1.
I select the setting in the camera's setup to automatically save to Ext SD.
Problem 1: it's doing fine most of the time in saving the picture, but intermittently it lost half of the image. So I literally can't see half of the picture. It's just greyed.
Problem 2: when I delete some photos, it's successfully removed. I can't see it anymore in the Gallary. Then after awhile (i don't remember how long, just when next time I open Gallary, viola they reappered).
I don't have sync with Google Drive option, I have "upload to DropBox" enabled. As far as I know, it uploads to DropBox but never downloads or sync it.
any advise?