Safari - annoying popups

[jonb108]

I'm using Safari 13.1.1 on my MacBookPro running OSX Mohave 10.14.6.

I have blocked popup windows on all sites in the Safari Preferences dialog: Websites > Popup Windows.

But still when I go to various sites a kind 'preview' of the site appears.
I need to choose Escape to have it go away. This is quite annoying.
It just happened on this site: [link removed]

Any clues for me?
Thank you very much!

[Turboladdade]

If you're experiencing unusual popups I would suggest first scanning your Mac for any malware or adware using Malwarebytes

[chasm]

What Turboladdade said, but also report it to the webmaster if that’s the only site that gives you that pop-up.