All quotation marks have disappeared

This morning, I started back to work on my manuscript, and a few minutes in, i noticed that all my quotation marks have disappeared. I’ve used scrivener for many years and have never had this happen. Anyone have any idea what’s going on?
I tried the usual undo, after copying out what I’d just written/added, to no avail.

UPDATE: I found the backup from last night, unzipped and opened it, and the quotations are showing again. WHEW.
But that doesn’t answer the questions: why did this happen in the first place, and how do I prevent it from happening again?

Did your apostrophe’s also disappear?
Do you still have the deviant version, and if so, are the quotation marks back in that version too?
Do you use straight quotes or smart quotes? Theoretically, you could delete all quotations in one go if you did a project replace and you were using straight quotations.
I’d assume an incorrectly stated regular expression (RegEx) could do it, too.