The typical response to the ORA-1555 errors with Automated Undo is to increase the value of UNDO_RETENTION. But it appears that you are still losing information. Check the UNXPSTEALCNT and NOSPACEERRCNT columns of V$UNDOSTAT as well. A non-zero value in any of these columns means that your UNDO tablespace is not large enough. You can rebuild your UNDO tablespace to be uniform extents of 1 MB each and see if that makes a difference. Additionally, you can increase the values of your TRANSACTIONS and TRANSACTIONS_PER_ROLLBACK_SEGMENT parameters. Automated Undo uses these two parameters to help in determining how to handle undo segments. Query V$RESOURCE_LIMIT to see if your maximum number of concurrent transactions is higher then the TRANSACTIONS parameter. Make sure that TRANSACTIONS is greater that what V$RESOURCE_LIMIT tells you.
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