Well, ive seen it across three operating systems (Linux, windows, android). So if you've seen it too on Mac/safari, its safe to say its probably a site specific integration. Hopefully unlock origin adds a blocker for it (though definitely not guaranteed as its not technically an ad). In the meantime, might be worth adding a specific block for the pop up element in UBO. Though not sure if the latest safari has UBO support so I don't think that helps you.