Strange empty graphic shows up on category archives

I cannot for the life of me figure out a way to fix this. I’m running a Project AR2 theme at anthracitefields.com. When you use our ubermenu bar and get a category listing like https://www.anthracitefields.com/wp/category/partners/ you get a blank graphic before the first thumbnail image. When I look at the code, it looks like someone has compromised a plug in or some of the wordpress code. I see a listing for a site xanderle.de. I don’t see how this got here or where it’s coming from, much less trying to fix it. Any and all suggestions are helpful. Thank you so much.