I guess this problem has nothing to do with your recent Android (MIUI) update to Mi4 smartphone. Please make sure you have not selected the "Guest" mode with a bell icon in your notification bar/status bar.
In Guest mode, MiUi users will not able to see gallery images, nor they can see the captured images from the camera app. Even if you install third party camera apps, those photos will not be visible. Please reply after checking it.