Randomly dropped
1, Unplug the external network cable, there is a drop condition. If it is normal, it may be caused by IP conflicts, etc. You need to check whether the IP conflicts, change the new IP address and try again. Still dropped, restart the NVR to see if it is dropped
2, Upgrade NVR and cameras to the latest version, please send your version of NVR and cameras to the support. After the upgrade, observe the results. 

Fixed channel dropped
1, Check whether the network cable under the current channel is too long, whether there is interference, whether the code stream value is too large 

2, Swap camera, After the replacement, there is still a possibility of drop, please reduce the camera resolution or upgrade the camera.