I constantly run into issues where features are planned and broken down outside-in, and it always makes perfect sense if you consider it in terms of the pure user interface and behaviour. It completely breaks down when you consider the API, or the backend, is a cross-cutting concern across many of those tidy looking tasks and cannot map to them 1:1 without creating an absolute mess.
Trying to insert myself, or the right backend people, into the process, is more challenging now than it used to be, and a bad API can make or break the user experience as the UI gets tangled in the web of spaghetti.
It hobbles the effectiveness of whatever you could get an LLM to do because you’re already starting on the backfoot, requirements-wise.