Strange URL in search console reports

We fixed some issues according to the Google Search Console reports. However, we came across a problem that we do not know where to look.

As you can see in the image, Google is exploring pages with a URL at the end that has never been created. The URL is not our domain but it is one of our clients that we used to follow their web banner with GA. We removed this banner a very long time ago with the Google tracking code.

(We use WordPress and follow banners with HTML added in widgets.)

search console report

If you have something in mind about this question, thank you for letting me know.

I've looked at the site map and there are no URLs of this type either.
Thank you