I recently was working on transitioning a Python script used with ArcMap 10.3.1 to run Data Driven Pages and export map pages to individual PDFs to an updated script that would do the same thing in ArcGIS Pro 2.1.1 with Map Series. During the update, I had a reoccurring issue with the variable I assigned to the list of layouts in the ArcGIS Pro project coming up empty (Print() function returned 'None'). In each of those cases (across a couple different project files and different index layers), I had an active Layout view and the Map Series functionality had been activated prior to running the script. After some additional testing in a completely new project file set up and all, I no longer had these issues. I did work with Esri Tech Support on this briefly and they were not able to recreate the issue with their data.
I was curious if anyone else had encountered this particular problem? I would like to determine if there is a discernible pattern and thus if there is a bug somewhere that needs to be reported.