Why have my doents in my Drafts file suddenly started to disappear?

Why have my doents in my Drafts file suddenly started to disappear? I have many "model" emails I sent over and over, needing only to change a few details. I leaver these in my Drafts and use over and over, but as of late, they keep disappearing!!! I would like this to stop as I spent much time replacing them today and tonight they are gone again!!!! What can I do to prevent this from happening anymore?