I don't see any errors in your configuration. Please check the classes and its inheritance , may be you are missing some class. I have implemented the same thing and I didn't face any issues. Please try it once again and if not coming again, verify the classes.
I tried creating similar use-case in my local environment and could observe the section was appearing as expected with the data of the data page as well.
For sure, I feel the data page isn't loading probably or isn't available at the time of DOM creation.
Please verify it by seeing on the clipboard under Data Pages subheading(as below):-
If the data page is available and the section isn't appearing in the UI. Please replicate the issue and capture it in tracer and share here(Make sure you have selected "Stream Rule" option in settings configuration of tracer).
Alternately, you can also invoke data page in the flow rendering UI either by calling an activity or data transform in pre-processing of flow.