Un commanded 5 star rating

It took the Organizer about 15 seconds to select all 260k images in my catalog with a Ctrl+A command.

I'm pretty sure that the star ratings are held within the catalog's database file.  So, it might be  worth trying to restore a backup catalog.  Or simply open the older catalog if that is just a copy.  (It wasn't clear what you meant by archived.)

I'm not sure how Elements handles star ratings if the metadata has been written to the file.  You can probably figure it out by creating a small sample catalog.  If you're not sure what I mean, I will try to perform the experiment later today when I have some time.

And, yes, the auto create feature does have some unusual results. But it has also saved me time with a lot of projects.

I have never heard of such a thing happening before.  The only way I can see that happening is if you accidentally selected all images in the grid and hit the star rating or pressed numeral 5.   Or, like some other user recently commented about another problem:  the cat did it. 

I understand that you don't want to go through your star ratings again.  Perhaps use the Auto Curate feature to find your best photos.