I just had this happen to me and found a solution to reclaim most of the latest version of the PDF:
-Open your PDF in Acrobat,
-Go to "Save As Other,"
-Save it as a PDF/X.
-Open that PDF/X in Illustrator, there will be a prompt asking if you want to keep or discard the changes made outside Illustrator.
-Click "Keep the changes" and the file should open to the latest version.

I did notice that all lines of text have been separated, but that's relatively easy to reconstruct.

I've come across this issue occasionally. My best guess is that when you open the PDF in Illustrator and save it as a new PDF with whatever changes you made, the file become embedded with 2 sets of data: "PDF Data" and "Illustrator Data". Acrobat and Preview etc view the "PDF Data" while when you reopen it in Illustrator, it just views the "Illustrator Data".Solution: Open the PDF in Preview, hit Print, and in the bottom left of the Print window select PDF and then Save as PDF. This new PDF document should be saved with just the data of what you see in Acrobat/Preview, and when you open it in Illustrator it should be that same data. Occasionally when you do this trick, the text will come into Illustrator all garbled. As a best practice, you should ideally only be working from the original Illustrator file and not PDFs, but if you must, when you first bring in the PDF into Illustrator to edit, save it as an Illustrator file so you have that good version, and out put as a PDF to send etc, but always work from the Illustrator file.

I also am having issues, have had to rebuild the same file more than six times now. It makes me scared to close ANYTHING. Would love some help if anyone has found out anything.

Has anything been done about this???
It wouldnt even be so bad if all the work was lost but it only lost some changes and not others!

Hello Illustrator Team!!!

Hi everyone, same thing happened to me, but I fixed it by deleting the excess artboard. I also saved the pdf over the bad file. Hope this will help you too, please do tell if it does.

I chatted with someone in Adobe about this issue, and they believed that this happened because I didn't work locally on my computer, but on a drive. They believed this was the issue. I also worked in a PDF instead of illustrator-file, in illustrator. And now to avoid the issue, I started working in AI-files instead.

Other than that I didn't get any solutions to this problem I'm afraid.

This just happened to me, too.

Same issue here and its driving me insane! Please help!

Same issue here. Please provide a solution!

I have the same issue... Worked on a project twice before I noticed it wasn't me that was going crazy.

This same thing just happened to me, what the heck!!!! I restarted my computer hoping that would fix whatever is going on. Didn't help. Opens correct in Photoshop, acrobat everywhere but where I need, Illustrator!

Same thing happened to me twice now! This is absolutely unacceptable and needs to be resolved!!

This is totally unacceptable!!!

Same problem!! Hours of work lost and I'm on a deadline! Not the first time this has happened either!

Is there a fix for this?

I also have this problem. Saved my work throughout the day, leave the office, come back the next morning and when I open the file...it's old work. It's not saving the most recent changes. I've had this problem in Illustrator and Animate.

I have the same problem with illustrator, but also with photoshop and indesign.... When i save while working on the illustrator, photoshop or indesign file it reverses my save while i am working on it! Real frustration for me when i work for school projects!

I got the same problem!! Did you fix that?

I'm experiencing this same error. Illustrator displays an older version of the PDF when opened, but even Adobe Acrobat shows the correct recent version of the PDF when opened.

I've tried renaming the file, but that doesn't solve it.