Double headers in checkout page (bug?)

Hey! I found some issue with WixStores’ checkout page. I work in Editor X and, as you can see on my screens, apparently, wix doubled my header, the point is that checkout autogenerated header by itself and I don’t have any idea how to fix it… What could be the problem?

P.S On the second screen I deleted checkout iframe to see how does it work.

Can you try this.