In iOS builds, sometimes Unity cannot open files contained in the Data folder. The problem is inconsistent, sometimes it is able to open a file but later the same file cannot open. Also, it works correctly in the editor and Standalone-Mac builds.
Sometimes it fails to open an asset file, when this happens there are missing textures or prefabs fail to instantiate. The XCode log might look like this:
Could not open file /var/mobile/Applications/E52F70F0-C857-4583-9C77-F8A0E50A5D21/XXX.app/Data/sharedassets40.assets for read
Sometimes if fails to open a level file, when this happens the app freezes. The XCode log is:
Could not open file /var/mobile/Applications/E52F70F0-C857-4583-9C77-F8A0E50A5D21/XXX.app/Data/level39 for read
When I log the files contained in Application.dataPath and its subdirectories, all the files are logged even after the error occurs. This suggests that the files are copied to the device but then sometimes fail to open. Sometimes a file opens normally a few times before the same file is unable to open.