Subflow isn't using the current Run-As setting when executed from within a flow, but it will if you force the parent to be re-activated (see workaround for details).
Steps to Reproduce
Login to any of Madrid, Newyork family instance
Navigate to 'Flow Designer' > Designer
Open the below flows
>"Check if comment is added by others"
> "Update case when Needs attention field is toggled"
Click on 'Properties'
Change the 'Run As' to 'User Who Initiates Session'
Click on Save >Publish
Now Navigate to sn_customerservice_case.list
Create New case
Update the case 'Additional Comments'
Now go to audit history of the created case
Check the audit line for 'Action Status' updated by column value
It should be the user id/name who updated the additional comments but it will show as 'system'
Make a benign change to the parent flow and re-activate it (just De-activating and Activating won't work).
Related Problem: PRB1386019