Using a Chromebook with Chrome.
I only have two notebooks. When I tried to change notebooks to add a new entry, the dropdown did not have the 2nd notebook.
When I do a search of a tag I know I wrote in the 2nd notebook, the note appears with the 2nd notebook name. When I select the down arrow in the drop-down, the 1st notebook name is gone.
I deleted the Notebook Web extension in Chrome. Closed Chrome. Downloaded Evernote Web. Opened Evernote and it appeared. The extension listing is still gone. The 2nd notebook does not appear, yet all my notes seem to be intact.