I have a small site that has dropped totally out of top 100 rankings.
When I did a site: command to see if there were any issues, I found 25% of the listed pages were duplicated with exactly same url. (I have checked over and over again).
I have never seen the same page listed more than once before directly under each other.
Clearly if Google is seeing these as different pages, this would explain the loss of rankings, but when I click on one of the urls, both urls are highlighted as clicked on, confirming these are identical urls but listed as duplicate.
Clearly there are changes or issues within the index