I think it's the application of Scrum to work that doesn't primarily fall inside the (Cynefin) "simple" domain-type work that Scrum was designed for.
It's fine if the work is straightforward and easy to estimate. But, if it isn't, things get problematic. There are three variables that interact with each other when working on a project: time, scope, and quality. If you pin down both your acceptance criteria and the time you have to implement (which is basically what happens in a sprint planning meeting), then quality is the only remaining variable you have to manipulate when things aren't going according to plan.