This is during our 3rd flight after the supplier trained us on this particular drone. During training we flew 3 other successful missions. We were using waypoint mission mode where in we had drawn a 20 hectare rectangular area. According to our drone supplier, all sensors were set in the ON mode when they trained and handed the drone over to us. We had set the mission altitude to 100 meters and return to home altitude at 120 meters. We are certain that the terrain we flew in, had no tree or any other obstructions/obstacles at that altitude.
As the drone took off for the waypoint mission and started to fly towards the "S" ikon in the DJI GS4 application, we lost the signal with the drone. This happened almost in 10 - 15 seconds of the mission start time. The green light on our remote controller went red. We expected the drone to come back to where the drone took off from. But later when we talked to a few people who saw the drone go above them, they explained that the drone reached one point, stopped and then started to decent at a normal pace. By this time we were concerned and started to walk towards the direction of the drone. At one point we got the connection back at which time the error message "MC board has lost transmission" was showing up on the app. While we were walking we lost and received the signal once more. At this time the camera was not giving any image. At one point, the error message "rollover detected" appeared on the app. After few minutes, for a brief second, we received an image on the screen of the drone resting flat on the ground but in thick vegetation/bushy area. We understood that it has crashed.
We continued to search for the drone. Meanwhile the battery of the drone died off completely. When we found it, it was 180 degrees turned, upside down. There was no severe externally visible damage other than few scratches on the propellers. We didn't do anything to the drone afterwards and right away took it to our DJI authorized service center.
We purchased the drone on December 2020 and received our drone on 12th of February 2021 and this mission was conducted on the 26th of March 2021. So the drone is brand new and was flying with a fully charged battery. We strongly feel there was some issue with the drone firmware or software which led to this failure. We checked the images and they concur with what the people who saw the drone landing, told us. The images are one by one closer to the ground until the last image which shows the drone almost 10m above the ground. We feel it has gone to the "S" point and automatically descended/ landed in an area where there were thick bushes.
Our local DJI dealer/service center has told us there was a faulty sensor on one of the legs of the drone and that it has to be replaced. They also informed us, during their trial tests after fixing it they are hearing a strange and abnormal noise. So we requested them to do a thorough inspection. We informed them that we would only take it if DJI is fully confident it can be flown safely without any issue in future.
Please help us get this issue resolved as this is a brand new drone (5th flight) and from our part, there has been no error since the mission was planned meticulously checking all the parameters at least twice. The supplier is indicating us that we would be charged for some sensors and other things. There is no possibility what so ever that it has struck anything, as the terrain is definitely not close to nor above 100 meters. We know that the drone has gone and tried to land at some point other than the home point, sometime during the mission.

Hello there vineethpandalai. I am sorry for the trouble this has caused and thank you for reaching out. Since this unfortunate event and there was a crash that happened to your DJI Phantom 4 Multispectral before. It would be best to contact our DJI Support Team at https://www.dji.com/support for us to be able to assist you further with regards to this matter. Again, I am sorry for the trouble and thank you.