rqt_plot not plotting one signal; rostopic echo works

edit

Hi,

I want to plot 2 signals: desired velocity and current velocity. Both come from a Twist, and I want to plot /linear/x. I try with rqt_plot and it can successfully plot the desired velocity, but not the current velocity.

Please have a look here: https://imgur.com/a/bTqXF

However I can see the topic is being correctly published with rostopic echo:

$ rostopic echo /current_velocity/twist/linear/x
1.7227491072e-08
---
1.7227491072e-08
---
5.7998790784e-07
---
6.097357376e-07
---
5.9487299872e-07

What's the problem? Thanks!