Microservices Demo: no services interconnection in Zipkin UI

[NorthCat]

I am trying to run Microservices Demo. After doing all the operations, when I open Zipkin UI, I see the following:

5 single traces instead one, no services interconnection.

But I was expecting something like this:

I don't really understand what I am doing wrong. Can anyone please help?

[NorthCat]

I figured out what the problem is. 5 single traces instead one were obtained if I used python 3.6. When using python 3.7. everything works fine.