Test email hangs

Hi,

Today I did the installation of two WP sites.

These two sites have the same configuration: same plugins, same theme, etc.

I am using a plugin named FluentSMTP to send email from WP, to use each server’s SMTP. These 2 sites are on the same server.

On both accounts, the sending tests, carried out earlier, worked. But now only one of the two sites is able to do this test.

You can see it in my video capture here: https://www.awesomescreenshot.com/video/3021544?key=e1573e1d1398edf99ce1087549b8a7bd

Is there something I can do to find out the reason why it hands now?

Thanks,
Phet