Oracle DB Query timeout when using Group By clause

I have a comprehensive SQL with many nesting Subqueries. At the end on nesting sqls I use Group By statement.

The query can not run (take very log time untill timeout).

However when I remove group by statement, query can return 500k rows in several minutes.

Execution plan shows that it takes 76% CPU time on HASH GROUP BY and 16% CPU time on HASH JOIN RIGHT OUTER.

Please help to solve the problem.

It should be an execution optimazation problem of Oracle DB.