BUG #15528: on v11.0 version still get error "ERROR: catalog ismissing 1 attribute(s) for relid 6855092" - Mailing list pgsql-bugs

The following bug has been logged on the website:

Bug reference:      15528
Logged by:          zhou xiaowei
Email address:      110876189@qq.com
PostgreSQL version: 11.0
Operating system:   Linux 3.10.0-327.36.58.4.x86_64
Description:

Hi,my friend.
I dump out 27969 tables from PG v9.6.8 one by one, use "pg_dump -t xxx -f
xxx.sql". Then start 300 threads to parallel import these .sql  into
v11.0.
after data imported completely, parallel create constraint for every
table.
when all completely, execute "vacuum full",I got error "ERROR:  catalog is
missing 1 attribute(s) for relid 6855092", which occured on 11beta2 solved
by BUG #15309.

Today, I want to make sure which step cause this issue, I only start 300
threads to parallel import these .sql, not create constraint for them.
when execute "vacuum full", I got error "ERROR:  duplicate key value
violates unique constraint "pg_class_relname_nsp_index""
the details:
ERROR:  duplicate key value violates unique constraint
"pg_class_relname_nsp_index"
DETAIL:  Key (relname, relnamespace)=(pg_toast_17589_index, 99) already
exists.
STATEMENT:  vacuum full;

after "vacuum full" error,I got different info about pg_toast_17589_index
from pg_class:
ncc_1126=# select relname from pg_class where relname =
'pg_toast_17589_index';
       relname        
----------------------
 pg_toast_17589_index
 pg_toast_17589_index
(2 rows)

ncc_1126=# select * from pg_class where relname = 'pg_toast_17589_index';
       relname        | relnamespace | reltype | reloftype | relowner |
relam | relfilenode | reltablespace | relpages | reltuples | relallvisible |
reltoastrelid | relhasindex | relisshared | relpersistence | relkind |
relnatts | relchecks | relhasoids | relhasrules | relhastriggers |
relhassubclass | relrowsecurity | relforcerowsecurity | relispopulated |
relreplident | relispartition | relrewrite | relfrozenxid | relminmxid |
relacl | reloptions | relpartbound 

----------------------+--------------+---------+-----------+----------+-------+-------------+---------------+----------+-----------+---------------+---------------+-------------+-------------+----------------+---------+----------+-----------+------------+-------------+----------------+----------------+----------------+---------------------+----------------+--------------+----------------+------------+--------------+------------+--------+------------+--------------
 pg_toast_17589_index |           99 |       0 |         0 |    16396 |
403 |     1739800 |             0 |        1 |         0 |             0 |
          0 | f           | f           | p              | i       |
2 |         0 | f          | f           | f              | f              |
f              | f                   | t              | n            | f
         |          0 |            0 |          0 |        |            | 
 pg_toast_178529      |           99 |  178537 |         0 |    16396 |
0 |     1807123 |             0 |        0 |         0 |             0 |
        0 | t           | f           | p              | t       |        3
|         0 | f          | f           | f              | f              | f
             | f                   | t              | n            | f
       |          0 |        96029 |          1 |        |            | 
(2 rows)

two querys got different content for column 'relname'. 

.sql's content as follow:
--
-- PostgreSQL database dump
--

-- Dumped from database version 9.6.8
-- Dumped by pg_dump version 9.6.8

SET statement_timeout = 0;
SET lock_timeout = 0;
SET idle_in_transaction_session_timeout = 0;
SET client_encoding = 'UTF8';
SET standard_conforming_strings = on;
SELECT pg_catalog.set_config('search_path', '', false);
SET check_function_bodies = false;
SET client_min_messages = warning;
SET row_security = off;

SET default_tablespace = '';

SET default_with_oids = false;

--
-- Name: hrtm_myquestion; Type: TABLE; Schema: ncc_gh; Owner: ncc_gh
--

CREATE TABLE ncc_gh.hrtm_myquestion (
xxxx
);

ALTER TABLE ncc_gh.hrtm_myquestion OWNER TO ncc_gh;

--
-- Data for Name: hrtm_myquestion; Type: TABLE DATA; Schema: ncc_gh; Owner:
ncc_gh
--

COPY ncc_gh.hrtm_myquestion (......
\.
--
-- PostgreSQL database dump complete
--

what happened? is this a bug?
To get more details for this issue, how can I do it?