you mention that you noticed this after your monthly backup. Do you still ahve the original file? If so you can check the source file and see if the source file has the same issue. If so the source file is the issue. if not you can delete the corrupted file and restore the original.
If you no longer have the source file this is not technically a backup. a backup is only a backup if there is more than one copy of the file. if you are using the iXpand to free space on your phone and then deleting the source files you should be backup up the ixpand to a computer. If you are not doing this you do not have a backup you only have the files.
data corruption can occur during capture, during transfer, or during storage and can occur for dozens of reasons. Data corruption is not necessarily a problem with the storage device. This is one of the many reasons why having more than one copy of data is important.
