I have a whole generation of phone's worth of photos on my phone, which i recently transferred to my otherwise fine Sandisk SD card two days ago, which happened to be just after updating my Sony Xperia Z3 compact to Android 5.1.1.
Now I have this exact problem http://androidforums.com/threads/xperia-corrupted-photos-lost-dir-sd.725157/ whereby the files are still on my card but have found their way to the LOST.DIR folder and have no file type, so no app can read them. They should be a mixture of file types, including many jpegs and some movie files, which have all retained their file size, but can't be read.
I don't know if this is because something in the OS isn't finding an extension that would recover them, but I don't think it's a corrupt sd card. I have tried Dr.Phone and PhotoRecovery, but it's not necessarily about recovering them, just recognising them.
I'm not the first to encounter this, but I don't understand if help offered to other people has helped, or particuarly how to do it anyway. Any thoughts or Eli5 explanations appreciated.