Adding row to nested DataGrid, how to notify parent

Hi there! I have a DataGrid that can be expanded to edit related nested rows. I'm having trouble getting the parent to be aware of the newly added or modified rows in the nested grid. If I collapse and expand the nested grid, the nested grid shows the nested grid in its previous state. If I refresh the whole page, then I see the updated content as expected.

Here's a little walkthrough!AvguHRnyJtWMme5Y-eJaF974OeYgPQ?e=qY9pgM

I've tried several things with EventCallback, EventCallback, and I tried this Stack Overflow suggestion
but couldn't get it to work. Any ideas?