The RealSense D435 RGBD camera is generally very robust and reliable. It can however fail to connect and display the image and depth frames. When this happens, hardware notification errors appear in the realsense-viewer software as shown below.
Usually this is caused by a connection issue, such as trying to use USB 2 with the RealSense, since it strictly requires USB 3. It can also mean that something has gone wrong with the camera’s internal settings or software, in which case a firmware upgrade is necessary.
To proceed with a firmware upgrade, download the latest firmware for Intel RealSense D400 product family. This is a .bin file with some documentation. Proceed with the official linux installation guide. Once that is completed, restart your computer, reconnect the RealSense camera and open realsense-viewer to display the camera streams.