<param name="Rtabmap/TimeThr"           type="string" value="700"/>

When updating the map requires for than 700 ms, some nodes in the map will be transferred to Long-Term Memory, making some parts of the map disappearing. However, if the robot navigates again towards these areas, they should re-appear (e.g., like if the robot remembers previous areas). If Rtabmap/TimeThr is 0 (disabled), you will keep always the full global map, but at cost of not having map updates done online (more and more time is required to update the map). You should see info messages on terminal telling the current processing time used for map updates.