Getting ORA-01555 while no space pressure on UNDO tbs nor max query exceeded UNDO_RETENTION

When running dbms_sqlpa, we encounter snapshot too old but we didn't see any issue with free space nor long query duration, we keep running into the same issue (3x) although nothing else running in database except dbms_sqlpa.

SQL> begin dbms_sqlpa.execute_analysis_task(task_name => 'SPA_RAT_C361_R5_FULL', execution_type => 'TEST EXECUTE', execution_name => 'AFTER1-RAT_C361_R5_FULL', execution_desc => 'Creating After1 Trial for SPA_RAT_C361_R5_FULL', execution_params => dbms_advisor.arglist('sqlset_name','SQLSET_RAT_C361_R5_FULL','sqlset_owner','SYS')); end;

/

begin

*

ERROR at line 1:

ORA-01555: snapshot too old: rollback segment number 6 with name