Hi Leon, I have an idea: You could could create a helper entity called 'indicationSelectionHelper.' Make a many-to-many association between indicationSelectionHelper and Indicators.
In your selection microflow for the list of Behaviors, pass in the list of behaviors into a microflow. In the microflow, create a new indicationSelectionHelper entity. Then iterate through the list of behaviors and retrieve all indicators for each behavior. Associate the list of indicators to your indicationSelectionHelper using the 'Add' option for the reference set.
On the next page, you can have a data view to which you pass the indicationSelectionHelper. Inside that data view, put a Data Grid of indications and populate it over association to the many-to-many association between indicators and indicationSelectionHelper.
This will give you a data grid that contains all the indications associated with the behaviors you picked on the previous page. My guess is that the error you are getting is that you are trying to write an x-path constraint that contains a list as a variable.
Hope this helps!