https://www.theverge.com/2018/10/19/18000482/google-pixel-2-3-camera-photos-saving-bug-issue

Some owners of the new Google Pixel 3 and 3 XL are experiencing an issue in which taking a photo using Google Camera occasionally fails to save. Users on Reddit and Google’s support forums are sharing their experiences, and the issue appears to be widespread, affecting original Pixel phones as well as the Pixel 2 / 2 XL. Several members of The Verge’s staff who own Google Pixel phones have confirmed they’ve experienced the issue as well.

The issue occurs specifically in cases when the user takes a photo with Google Camera, and switches to another app or locks the phone immediately after. Users are able to see a thumbnail of the photo in the Camera gallery circle, but upon tapping it, the photo disappears. In some occasions, the photo doesn’t appear at all at first, but it will reappear in their gallery a day later.