Yesterday I lost a document on which I spent many hours. Today, I learned why. This may help others, so I am sharing it.
When you download an email attachment, you MUST save as. Just clicking save WILL NOT WORK. The computer will try to save it back to the email, which it is unable to do. You will not get an error message!
So download the file, save as, and then get to work.
I do this as standard (except, apparently, yesterday), which is why I had never noticed this issue before.
@Maswala Saving attachments. It depends on your email client. Thunderbird you just click "Download" and it saves to the folder of your choice or the standard folder.