The biggest problem with Kanban is that it‘s designed for a world where things go through the line once (e.g. a carmaker).
This got me thinking about whether the problem is generally with Kanban's use in software or instead the kinds of software development Kanban that is more useful in. A service firm builds a single use or single customer tool while a product firm builds a multiple use or multiple customer tool. A service firm tends to have more tasks around the missing parts of the software while a product firm tends to more tasks around the bugs in the software. For a service firm the factory is the assembling of the parts. For a product firm the factory is perfecting the assembly. I am mostly thinking aloud here but I think it is a useful train of thought as to why Kanban works for some firms better than for others.