Hello, @feeldesign,
Alright, I have added the countries list that you shared with us, on your site and I saved it. You can see in this video: https://streamable.com/gv58mi that it saved successfully.
As I told you in my previous message that the country appears randomly on your site infects you choose some specific list of countries and it is possible that there must be a third-party plugin that conflicts and causes the issue. But you said that you are not able to add specific countries so I add it for you.
Regards 8Themes Team.