From digging around, I’ve sort of narrowed down the number to be related to the .xaml structure. However, I don’t know how to extract it during actual run (only in debugging).
I’m keen to see if anyone else has a way of getting this as it would be super useful to pinpoint things with. There seems to be a improvement suggestion for something similar here: Activity Uid in case of application exception
and here: Component/Sequence/Workflow Name