Issue when insert data with ORDER BY on table with UNIQUE INDEX

Hello all,

I have an issue when try to insert some data into a table that having an unique index. Bellow is my situation:

1. I have a source table SRC_TABLE and have 10000 records.

( SEQ_NUMBER NUMBER(19,0) INVISIBLE GENERATED BY DEFAULT AS IDENTITY ORDER NOT NULL,

"col_1" NUMBER(8,0) DEFAULT ON NULL 0,

"col_3" NCHAR(1) DEFAULT ON NULL ' ',

"col_4" NCHAR(7) DEFAULT ON NULL ' ',

"col_5" NCHAR(3) DEFAULT ON NULL ' ',

"col_6" NUMBER(8,0) DEFAULT ON NULL 0,

  PRIMARY KEY (SEQ_NUMBER)

   ) ;

This table already have unique index as below:

CREATE UNIQUE INDEX "SRC_TABLE_UNIQUE_IDX" ON "SRC_TABLE"

  (CASE