Able to subscribe to topic but no output

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Hello everyone, I have a very weird problem while subscribing to a topic.

I have a bagfile containing this specific topic :

/radar_fc/parsed_tx/radartrack                                  395180 msgs    : delphi_esr_msgs/EsrTrack

It contains messages, so it looks fine.

But when I play the bag and subscribe or try to echo the topic, I get nothing. No error message, no error, nothing !

rostopic echo /radar_fc/parsed_tx/radartrack

rostopic info /radar_fc/parsed_tx/radartrack tells me that I subscribe to it correctly :

Type: delphi_esr_msgs/EsrTrack

Publishers: 
 * /play_1600094136880686877 (http://max-XPS:34781/)

Subscribers: 
 * /rostopic_8207_1600094360816 (http://max-XPS:40245/)

When I try rostopic hz I get an output :

rostopic hz /radar_fc/parsed_tx/radartrack
subscribed to [/radar_fc/parsed_tx/radartrack]
average rate: 1205.332
    min: 0.000s max: 0.059s std dev: 0.00480s window: 1144
average rate: 1200.979
    min: 0.000s max: 0.059s std dev: 0.00483s window: 2342
average rate: 1218.411
    min: 0.000s max: 0.059s std dev: 0.00475s window: 3597
average rate: 1227.879
    min: 0.000s max: 0.059s std dev: 0.00473s window: 3999

First I though that the message was not installed or compiled but when I do rosmsg info delphi_esr_msgs/EsrTrack to get the message information everything is correct :

rosmsg info delphi_esr_msgs/EsrTrack        
std_msgs/Header header
  uint32 seq
  time stamp
  string frame_id
string canmsg
uint8 track_id
float32 track_lat_rate
bool track_group_changed
uint8 track_status
float32 track_angle
float32 track_range
bool track_bridge_object
bool track_rolling_count
float32 track_width
float32 track_range_accel
uint8 track_med_range_mode
float32 track_range_rate

roswtf tells me there is an error but I don't understand where it comes from :

Found 1 error(s).

ERROR The following nodes should be connected but aren't:
 * /play_1600094136880686877->/rostopic_8207_1600094360816 (/radar_fc/parsed_tx/radartrack)

Do you have any idea what could be the problem ?

Thanks !