Altitude 0 m from KML auto changed to 100 m on WP

I am Harris Aerial H6 hybrid user. The left column is the altitude table with a flight height of 100m relative to the home point, which we set in the global mapper. the right column is the altitude on WP which is automatically input when loading kml in the mission planner. this is one of the lines that we sampled, there are still many altitudes that the mission planner converts from alt 0 to 100, and -2 to 0. Why only the alt 0 and -2 are becoming false mission planner altitude? But not on the -10 on kml that are correctly -10 on mission planner