Hi @Retired_mod 
Thanks for the quick response.
To clarify- no Unity Catalog asset of any sort is referenced or involved. There's no environment variables in play. We're not using Databricks-Connect, we're running a Databricks notebook via a workflow. We're not using any AWS services. We're on GCP, and also not using any GCP services.

We have discovered that this works on non-Unity Catalog clusters, or if we run the notebooks sequentially instead of in parallel.
We're not clear why running these notebooks in parallel on a Unity Catalog cluster is giving "credential scope" errors when there's no reason for any credential scope to be needed.