Hi, thanks for your response.  It doesn't seem to help at all, however.  The solution you suggest is what I've already done (including once more just now, to make sure), and it achieves the same outcome I've already described: 

• the parent run appears on my own experiment page with no children
• the child runs appear on the default experiment page with no parents

Let me try to provide a little more detail in case it's helpful. 

• My latest parent run has Run ID = `5e0500d99c9d41069138d9e10fe7e83e`
• Looking into one of the child runs, it has its own Run ID value and it has a field "Parent run" which points to the same parent run -- the value is a hyperlink to https://[redacted].cloud.databricks.com/ml/experiments/4161759641583557/runs/5e0500d99c9d41069138d9e... which points to that same parent Run ID.
• And yet, the child runs still show up in the GUI only on the default Experiment page, not grouped with the Parent run (which is still living by itself on my Experiment page with no children).

It looks somewhat like the `nested=True` parameter is doing a good job of getting the parent run ID assigned to the child run, but the GUI isn't honoring the parent-child relationship when it decides where to display the parent and child runs.

FOOTNOTE:  You mention setting `parent_run_id` without saying what to use it for.  Do you think there's a useful way to use it?  I created it only as part of a later experiment, to try passing it as an optional argument to the inner `mlflow.start_run()` call, but it didn't seem to have any effect on the outcome.