Repro steps:

1. Set "python.pylanceLspNotebooksEnabled" to true
2. Create a notebook
3. Create some cells that create a dataframe
4. Run the cell that creates the dataframe
5. Create a new cell to get members.
6. Type df.ag

Result:

Without python.pylanceLspNotebooksEnabled:

The root cause of this problem is the Jupyter extension is no longer creating the pylance server so we have no current way to query pylance for its list of completions to eliminate duplicates.

/cc @debonte