My previously fine AI files now open with this error: "Illustrator could partially read this file. We recovered as much of this file as possible, but some content might be missing. Open to view the recovered file". When I open the file, everything is missing besides for my first artboard (out of about 13 artboards - everything is gone??). I have a PDF of the file, saved. But it is a compressed PDF with editing capabilities, disabled. And so, am unable to work on/edit from the PDF.
Sorry to hear about your experience. There are multiple factors that can lead to file corruption. In addition to the suggestion given earlier, I'd request you to follow the suggestions given on this help article to troubleshoot file issues & let us know if it helps.