Rtabmap with Tango ROS streamer; rtabmap 'Did not receive data since 5 seconds!'

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Hello,

I'm running ROS melodic 1.14.3 on Ubuntu 18.04 64 bit (kernel: 4.15.0-45-generic x86_64 GNU/Linux) (and I'm a total beginner with ROS, don't hesitate to ask for more commands' outputs if needed).

I'm trying to map a room from an Android 6.0.1 Lenovo Phab 2 pro smartphone where I installed the "Tango ROS Streamer" application ( https://play.google.com/store/apps/de... ).

I can connect to the ROS Master on the laptop from the phone.
I can see incoming pictures from the fish-eye and the color cameras on the laptop.
I can see the live point cloud from Tango using $ rosrun rviz rviz -d /path/to/tango_config_file . The config file was downloaded from the link at point 2 of this page : http://wiki.ros.org/tango_ros_streame... , which is this one: https://github.com/Intermodalics/tang...

But when I try to follow the rtabmap + Tango tutorial from here: http://wiki.ros.org/rtabmap_ros/Tutor... I get stuck with 2 warnings.
From the previous webpage, everything is working up to point 4. I can see updates from the /tango/point_cloud topic.
Point 5 seems OK in a new terminal:

$ rosrun rtabmap_ros pointcloud_to_depthimage cloud:=/tango/point_cloud camera_info:=/tango/camera/color_1/camera_info _fixed_frame_id:=start_of_service _decimation:=8 _fill_holes_size:=5
[ INFO] [1551193102.094838430]: Initializing nodelet with 4 worker threads.
[ INFO] [1551193102.647795400]: Params:
[ INFO] [1551193102.647839474]:   approx=true
[ INFO] [1551193102.647929972]:   queue_size=10
[ INFO] [1551193102.647968631]:   fixed_frame_id=start_of_service
[ INFO] [1551193102.648015507]:   wait_for_transform=0.100000s
[ INFO] [1551193102.648036083]:   fill_holes_size=5 pixels (0=disabled)
[ INFO] [1551193102.648053149]:   fill_holes_error=0.100000
[ INFO] [1551193102.648071092]:   fill_iterations=1
[ INFO] [1551193102.648086249]:   decimation=8

And at point 6 I have two warnings printed every 5 seconds:

[ WARN] [1551193180.898167458]: /rtabmap/rtabmap: Did not receive data since 5 seconds! Make sure the input topics are published ("$ rostopic hz my_topic") and the timestamps in their header are set. If topics are coming from different computers, make sure the clocks of the computers are synchronized ("ntpdate"). Parameter "approx_sync" is false, which means that input topics should have all the exact timestamp for the callback to be called.
/rtabmap/rtabmap subscribed to (exact sync):
   /tango/camera/color_1/image_raw_relay,
   /image_relay,
   /tango/camera/color_1/camera_info,
   /rtabmap/odom_info

Followed by:

[ WARN] [1551193181.360817636]: /rtabmap/rtabmapviz: Did not receive data since 5 seconds! Make sure the input topics are published ("$ rostopic hz my_topic") and the timestamps in their header are set. If topics are coming from different computers, make sure the clocks of the computers are synchronized ("ntpdate"). Parameter "approx_sync" is false, which means that input topics should have all the exact timestamp for the callback to be called.
/rtabmap/rtabmapviz subscribed to (exact sync):
   /tango/camera/color_1/image_raw_relay,
   /image_relay,
   /tango/camera/color_1/camera_info,
   /rtabmap/odom_info

And an empty visualization rtabmapviz window.

I wonder if I must change something in the called rtabmap.launch file that was bunddled with the ros-melodic-rtabmap and/or ros-melodic-rtabmap-ros packages (I installed them with apt-get, they were not build.) ?

If this helps, here ... (more)