I started having this issue today. I am on Mac OS 10.13.6 It started when I could not open a note in a separate window. I often have several notes open in separate windows while doing research.
Then I found this discussion. I signed out of Evernote and then signed back in after a few minutes. Now all I see is a blank white screen of the last not I had been working on. Everything else has vanished on my macbook version. I am not sure how to go back to another version.
Between this issue today and not being able to email from evernote a copy of a note, this update has serious bugs. Very frustrating and wasting valuable time to troubleshoot.