BUG #15868: Creating foreign key fails to find data key that exists

The following bug has been logged on the website:

Bug reference: 15868
Logged by: Kurt Roeckx
Email address: kurt(at)roeckx(dot)be
PostgreSQL version: 11.3
Operating system: Debian
Description:

Hi,

I've dumped and and started a restore of a large database (the restore is
sitll in progress.) The data was in a 10.8 version, and it's being imported
in an 11.3 version.

The following 2 queries returned an error:
ALTER TABLE ONLY public.certificates
ADD CONSTRAINT certificates_raw_certificate_id_fkey FOREIGN KEY
(raw_certificate_id) REFERENCES public.raw_certificates(id);
ERROR: insert or update on table "certificates" violates foreign key
constraint "certificates_raw_certificate_id_fkey"
DETAIL: Key (raw_certificate_id)=(162071571) is not present in table
"raw_certificates".

ALTER TABLE ONLY public.ct_entry
ADD CONSTRAINT ct_entry_raw_certificate_id_fkey FOREIGN KEY
(raw_certificate_id) REFERENCES public.raw_certificates(id);
ERROR: insert or update on table "ct_entry" violates
foreign key constraint "ct_entry_raw_certificate_id_fkey"
DETAIL: Key (raw_certificate_id)=(521867241) is not present in table
"raw_certificates".

Both ids (162071571 and 521867241) exist in the raw_certificates table.

The id field looks like:
Column | Type | Collation | Nullable |
Default
--------------------+---------+-----------+----------+---------------------------------------------
id | bigint | | not null |
nextval('raw_certificate_id_seq'::regclass)

It's a rather large table. The data itself is about 2.2 TB, it contains
about 2G entries, the index on the id colum is 32 GB. Running the queries
above takes a very long time.

Kurt