Thanks for the reply. First of all, the image data used is a copy of a single image to make the specified number of copies. The same problem is also seen in iOS 10.0.1. The files that could not be read are being investigated using the following information. Data status (whether it is damaged or not) → I checked whether the file could be read by PhotoLibrary, and it can be opened and displayed normally. The data can be opened and displayed normally. → When I deleted all the data except for the data that could not be read, I was able to read all the data. So I guess the problem depends on the amount of data rather than the state of the data.