Some Pixel 2 and 2XL units do not save the pictures taken using Google Camera properly, so that they do not show up in Photos or in the phones' storage. This is now apparently happening to some newer Pixels as well. This issue may be linked to the HDR modes and how it processes photos.
https://www.notebookcheck.net/Some-Pixel-phones-are-not-saving-images-taken-using-the-Google-Camera-app.340711.0.html