I haven't done a whole lot with A/B Testing, but wouldn't the A/B Test page need to be a Sibling? Looks like it's trying to inherit it's other variant self.
A work around at minimum is you should go to your variant -> General -> Page Templates, and define the Page Template inheritance to skip it's parent (the original Shopping Cart) and inherit the root and levels 1 and 2 (or possibly just root and 2, depending on setup). This way it inherits the right page placeholder zones.