BUG #15528: on v11.0 version still get error "ERROR: catalog is missing 1 attribute(s) for relid 6855092"

The following bug has been logged on the website:

Bug reference: 15528
Logged by: zhou xiaowei
Email address: 110876189(at)qq(dot)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?