Attached is a zip file that I think will fix this problem.
For clarification, it is a bug (introduced by an error of my own) that does effect all sites. But unless you have a very complex tree (containing things like multiple relationships, and very large numbers of generations), you would not notice anything other than a slightly slower page loading. If you have nothing to compare with it would not seem like a bug.
In the attached zip folder are:
A complete replacement for kiwitrees/modules_v4/fancy_treeview_descendants. Just copy this straight over the existing module.
A replacement for kiwitrees/library/WT/Controller/FancyTreeView.php
Let me know if it works on your “historic” GEDCOM file OK.