Rtabmap deletes part of map

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I am running Ubuntu Mate 16.04 on Raspberry Pi 3 and have tried to build a map with rtabmap. I am using Kinect, fake lasermsg from Kinect, odometry from wheel encoders and imu. Rtabmap is running on the Raspberry Pi and the visualisation with Rviz on a remote computer. When the robot drives around, he builds the map quiet well but deletes these parts of the map, where he is not right now.

Launchfile:

<launch>

<!-- Connection + Driving: -->
<include file="$(find differential_drive)/launch/start_minimal.launch"/>

<!-- Urdf-Model + Transform: -->
<include file="$(find drink_description)/launch/load_urdf.launch"/>

<!-- Kinect + depthimage_to_laserscan: -->
<include file="$(find differential_drive)/launch/freenect_rtab.launch"/>

<!-- Robot_Localization (Combines Odom + Imu): -->
<include file="$(find drink_mapping)/launch/robot_localization.launch"/>

<!-- SLAM: -->
<group ns="rtabmap">
    <node name="rtabmap" pkg="rtabmap_ros" type="rtabmap" output="screen" args="--delete_db_on_start">
          <param name="frame_id" type="string" value="base_footprint"/>

          <param name="subscribe_depth" type="bool" value="true"/>
          <param name="subscribe_scan" type="bool" value="true"/>

          <remap from="odom" to="/odometry/filtered"/>
          <remap from="scan" to="/kinect_scan"/>

          <remap from="rgb/image" to="/camera/rgb/image_rect_color"/>
          <remap from="depth/image" to="/camera/depth_registered/image_raw"/>
          <remap from="rgb/camera_info" to="/camera/rgb/camera_info"/>

          <param name="queue_size" type="int" value="10"/>

      <param name="wait_fot_transform_duration" value="0.5"/>
      <param name="approx_sync" value="true"/>


          <!-- RTAB-Map's parameters -->
          <param name="RGBD/ProximityBySpace"     type="string" value="false"/>
          <param name="RGBD/AngularUpdate"        type="string" value="0.01"/>
          <param name="RGBD/LinearUpdate"         type="string" value="0.01"/>
          <param name="RGBD/OptimizeFromGraphEnd" type="string" value="false"/>
          <param name="Reg/Strategy"              type="string" value="1"/> <!-- 1=ICP -->
          <param name="Reg/Force3DoF"             type="string" value="true"/>
          <param name="Vis/MaxDepth"              type="string" value="4.0"/>
          <param name="Vis/MinInliers"            type="string" value="3"/>
          <param name="Vis/InlierDistance"        type="string" value="0.1"/>
          <param name="Rtabmap/TimeThr"           type="string" value="700"/>
          <param name="Mem/RehearsalSimilarity"   type="string" value="0.45"/>
          <param name="Icp/CorrespondenceRatio"   type="string" value="0.5"/>
          <param name="Grid/FromDepth"            type="string" value="false"/>
    </node>
  </group>
</launch>

Warning:

[ WARN] (2017-04-15 22:28:21.616) Rtabmap.cpp:1786::process() Rejected loop closure 803 -> 819: Cannot compute transform (cor=90 corrRatio=0.140625/0.500000)
[ WARN] (2017-04-15 22:28:21.626) Memory.cpp:1580::forget() Less signatures transferred (0) than added (3)! The working memory cannot decrease in size.