The following error appears at refresh:
F_JD20DB: DBMS error [ORA-08181: specified number is not a valid system change number].
Amazon hosted DB
Check the status of the manifest aggregator to make sure it is running and publishing.
When starting a refresh through the shell script, it invokes some database code that finds out how far ahead the manifest aggregator has processed changes. It uses this to align an SCN for the refresh and creates a job for it.
This setup is unique to Amazon. If the aggregator does not run or does not publish changes, then the script to create the refresh job ends up with an SCN that is too old for the database to still provide a consistent snapshot.