Holes/Empty spaces while elevation mapping and previous mapped points removed after the robot moves from that place

[Aishkrish18]

Hello,
I am currently performing elevation mapping in an environment which is similar to shopfloors.
I am using Orrbec camera to collect and use the point clouds from, and the pose from robot's encoders. While mapping around the environment, after cleaning the pointclouds, once the robot moves away from the mapped area, this area becomes empty or is filled with holes. After sometime, all the mapped area is removed and I am not sure, how to fix these two issues. Does anyone have an idea what parameters that could affect this?

Thanks!