Hi Maria,
Thank you for posting this. I looked at the workflow and it appears that the hang occurs when you set the X Step or Y Step to 0. I logged the following bug: [BUG-000124209: ArcGIS Pro hangs when Marker Placement X Step or Y Step is set to 0 pts.]
You can contact technical support if you would like to be attached to the bug. Otherwise, if you wait a bit and check back later, you should be able to find it on https://support.esri.com/en/ and click the Subscribe button.
Sorry that you ran into a hang - the development team will now review this issue.
Thanks