I'm not sure but probably after last software update I've got new folders where Viber photos and videos it's save. Usually they go to:
Internal storage\viber\media\Viber Images or for video \Viber Videos
Now it's shows two new folder where they go: Internal storage\Pictures\Viber or for video Internal storage\Movies\Viber.
I'm not use SD card, and when I'm check my chat history if I'm trying to open images is show "File Not Found"