I too struggled with this issue for a couple months. However, I was finally able to get a SharePoint Designer 2013 workflow to update all of the child items related to a specific parent item. Now, whenever a change is made to an item in the parent list, the SPD2013 workflow searches the child list for all the matching IDs and updates only those matching items. The workflow is surprisingly quick and when needed, I can run the workflow on 100 items at a time, with no performance issues. All 100 instances of the workflow complete before I can even get to the workflow status screen. This is a great way to keep 2 or more SharePoint lists in sync. If anyone is interested let me know and I would be happy to share the specs of my workflow.
This reply was modified 4 years, 5 months ago by David Jeremias. Reason: typo