Solution/Workaround: When this issue is seen, press Ctrl + E (windows) or Cmd + E (mac) or click the double arrows icon in top right 
. This bug is an issue with stuff being broken in the old editor layout view, like other recent bugs (1, 2).
If you see the double arrows at the top left you are in editor classic layout I believe. If you then press Ctrl + E (windows) or Cmd + E (mac) then it toggles the editor and the double arrows go away or is shown, when this happens this “phantom unsaved changes” bug goes away.