if you have any filters on the portal you should look into the script step refresh portal. Also look at the join criteria between the parent and children to see if anything involved is firing late.
There are no filters on the portal and the relationship is pretty simple, parent::serial number to child::client id.
if you put a "refresh data" button on the screen, which does a Refresh window with flush, do you get actual data displayed ?
I'm sorry to say that, but displaying correct data beats displaying it fast, so if it has to be, just put the refresh/flush as trigger and you're done.
I just tried putting a button to refresh the wind with flush and it didn't help.
After logging out and back in a few times the data was showing.