If you can do it through the psql prompt, then the problem is most likely pgAdmin4, otherwise you might want to get in touch with the postgreSQL devs/support lists.
For example, you can run the COPY command both with and without the HEADERS option and see if that works.
yes thank you I will scan the table so at least I will see the 'bad' characters. We will see how many there are.
Sorry, i forgot to append the data.
Thanks. Did that include the "bad" data? I can load it just fine into a SQL_ASCII database (which I'd expect, as there's no encoding checks), or a UTF-8 database, and I can successfully export the table in both cases.