The menu entry Maintenance->Statistics... actually rebuilds thumbnails. This seems to be a case of an incomplete removal of the Statistics dialog, as line 898 of MainWindow/Window.cpp renames the Action from "Build Thumbnails" to "Statistics...".
Now I see this was fixed in commit ce2479f18ca823c922805ef70a6e6e6d46b3d126 (2018-11-30). It just hasn't made it to the distros yet.