Report: No joy.
I added a [Delay] immediately after my [Add Instances] node and tested 0.0, 0.001, 0.01, 0.1, and 1. Unfortunately, it didn’t solve the issue.
Perhaps Blueprints have a different level of indirection that don’t execute exactly like the C++ equivalent functions.
Nonetheless, (as you alluded to in an earlier post) it definitely has something to do with the HISM tree not updating unless some other event tells it to refresh, in this case, the arbitrary clicking of the UE Editor borders, content browser list, tabs, menu items, etc.