I too am having the exact same problem when running Wall Charts, with options: Descendant Chart, 6 generations, bottom to top (which for reasons I don't understand generates oldest ancestor on top to youngest descendant on bottom).
My Version info is 18.104.22.168 running on MacOS 10.13.4.
My database is rather small (53 people) and all linkages appear to be correct. Box size and spacing is the default.
Upon generation of the chart, the horizontal connectors for different descending families cross on top of each other making it appear like many children belong to more than one set of parents. Moving the child boxes around will however reveal that they really are just connected to one set of parents. But it takes a lot of playing and shifting to figure out how to properly isolate the proper family groups (and that's only with a small tree). It would seem near impossible should this happen on a larger tree (not clear there would be enough "sheet size" to make the placements).
The problem is clearly that, for some users, the box placement on the wall chart is improperly being calculated in a way that horizontal connectors (across children) for one family overlap the horizontal connectors for the children of an adjacent family on the same generational level.
I also observe other box placement issues which may relate to the same positioning problem. For example, I observe the children for one family (let's call it the "center" family) are shifted so far left that they are more aligned under the adjacent parents on the left, and likewise, the children for the adjacent parents that fall to the right of the "Center family" are more aligned under this "center" family. I think it's this shifting that then generates extra long horizontal connectors which now overlap each other.