CREATE TABLE TEST_CI (
    RULE_ID INTEGER NOT NULL,
    CI VARCHAR(10) CHARACTER SET UTF8 NOT NULL COLLATE UNICODE_CI,
    ASCII VARCHAR(10) CHARACTER SET ASCII
);

INSERT INTO TEST_CI (RULE_ID, CI, ASCII) VALUES (1, 'А', 'A');
INSERT INTO TEST_CI (RULE_ID, CI, ASCII) VALUES (1, 'Б', 'B');
INSERT INTO TEST_CI (RULE_ID, CI, ASCII) VALUES (1, 'В', 'V');

COMMIT;

check query:

SQL> SELECT * FROM TEST_CI WHERE RULE_ID = 1 AND CI STARTING WITH 'А'

result: one record - is correct

Add the key (index)

SQL> ALTER TABLE TEST_CI ADD CONSTRAINT PK_TEST_CI PRIMARY KEY (RULE_ID, CI);

result: empty - bug