From Lightroom Journal:
Camera Raw 9.3.1 is now available through the update mechanism in Photoshop CC and the Creative Cloud application. This version fixes a bug that resulted in inaccurate tiles, such as black or white squares when not expected, when opening images in Photoshop. Please note that this bug typically only appeared when using both the Camera Raw plug-in and Photoshop for long running sessions.
Thank you for all your assistance in helping us find and fix this issue! Thanks!
Camera Raw 9 – Please select Help>Updates to use the update mechanism in the Creative Cloud app.
Please note – If you have trouble updating to the latest ACR update via the Creative Cloud application, please refer to the following plugin installation: http://helpx.adobe.com/x-productkb/multi/camera-raw-plug-in-installer.html