I agree, the closest modern equivalent is code that branches too much from too many places. Modern tools still help a lot to reason about it but it comes to a place where I, personally, have to create call flow diagrams on pen and paper or a whiteboard to actually understand some flows.

Code with extreme branching, while dealing with state/boolean parameters that determine flow branching; error handling that can also create other branches of execution; all of that is really hard to keep in mind when reading such nightmare codebases...