The way DJI has implemented cameras on the M210 requires that some cameras be connected to specific positions on the drone.
For more troubleshooting tips that may be helpful when using the Matrice 200 Series drones, see this article.
Single Sensor Setup
If you are only using a single sensor on a dual-mount setup, the most reliable setup is to use position I (on the right side as you are facing the drone). If using the Z30, there are cases where position II provides a more stable stream for the pilot, but the OpsCenter stream connection is less reliable.
Thermal Cameras
For thermal cameras, make sure the XT1 camera is always mounted in position II, or the XT2 is always mounted in position I.
Z30
If a Z30 is attached to position II, camera panning does not scale properly when the camera is zoomed in, resulting in difficulty tracking the image. To get around this limitation, you can use Tap Zoom to change the focal point. You will need to turn off Gimbal Lock in the Camera Settings menu for TapZoom to work correctly with this configuration.
The M210 drone also can encounter issues with pixellated video when using a Z30 as one of the cameras. When using this setup, try using the pill buttons to switch the feed to the FPV or Map and then back to the Z30. This can reset the image resolution in many cases.
X4S
If you are using an X4S camera, make sure it is connected to position I.