ORA-31603 On Dbms_metadata.get_dll For Dblinks Only

I have user U1 with dblink DBL1 (private dblink, not public).

CODECREATE DATABASE LINK DBL1
CONNECT TO U1 IDENTIFIED BY XX USING 'TNS1';

I have user U2 with dblink DBL2 (private dblink, not public).

CODECREATE DATABASE LINK DBL2
CONNECT TO U2 IDENTIFIED BY XX USING 'TNS2';

Both dblinks works fine, it means I can do select.

When I logged in with U1 and try to execute the following statement :

CODESELECT SYS.DBMS_METADATA.GET_DDL('DB_LINK',OBJECT_NAME)
FROM SYS.USER_OBJECTS
WHERE OBJECT_TYPE = 'DATABASE LINK'
AND OBJECT_NAME   = 'DBL1';

I get ORA-31603 error:

CODEORA-31603: object "DBL1" of type DB_LINK not found in schema "U1"
ORA-06512: at "SYS.DBMS_METADATA", line 4018
ORA-06512: at "SYS.DBMS_METADATA", line 5843
ORA-06512: at line 1

same happens when I pass user name to get_ddl:

CODESELECT SYS.DBMS_METADATA.GET_DDL('DB_LINK',OBJECT_NAME, [b]USER[/b])
FROM SYS.USER_OBJECTS
WHERE OBJECT_TYPE = 'DATABASE LINK'
AND OBJECT_NAME   = 'DBL1';

When I select from user_objects with the following query , it is there.

CODESELECT *
FROM SYS.USER_OBJECTS
WHERE OBJECT_TYPE = 'DATABASE LINK'
AND OBJECT_NAME   = 'DBL1';

DBMS_METADATA.GET_DDL works for every other objects of U1 (tables, views, ... for example) except for dblinks. DBMS_METADATA.GET_DDL works for every objects of U2, includes DBL2.

I tried to add "select catalog role" to U1, even when I know that I need it only for objects from other users.

I tried to create DBL2 in U1 - same results.

I tried to re-create dblink using full connection string - with same result.