DBMS_XPLAN.Display_Cursor() not working all the time

Oracle EE RAC on 12.1.0.2 (ODA X5-2).

Have a PL/SQL package creating a CTAS DDL and executing it dynamically (using execute immediate).

The very next statements executed are for instrumentation. Get the row count from the cursor for the table created by reading SQL%RowCount into a variable. Always works.

Then get the cursor's execution plan via DBMS_XPLAN.Display_Cursor().

It works fine most times. However, no execution plan is returned for specific CTAS DDLs that use a significant number of PQ slaves (32+) on significant data volumes (reading billions of rows via FTS). I tried alternative methods like searching thru the shared pool (e.g. using