FTP error that isn't?

I'm uploading my site using the built in FTP agent. I put in the hostname (hoc.org.uk), the username and the password. I get an error which says "host name does not exist". Well, I know it does because I used exactly the same parameters using Filezilla and that worked.

So, I ignore the error and click "Publish" and it all works OK and uploads my files.

What's going on?

Alan
[Running 16.2 on Windows 10 v1903)

I've no idea Alan, possibly something to do with with your site having an ssl certificate?

Could be. Filezilla didn't mind.

Anyway, the site loaded up OK.

Alan