I have seen many cases of Claude ignoring extremely specific instructions to the point that any further specificity would take more information to express than just doing it myself.
It’s often because the context is full, I gave a bad prompt or context has conflicting guidance either from direct or indirect (agents.md) prompts.
I spend 8-20 hours a day coding nonstop with agentic models and you can believe I have tuned my approach quite a lot. This isn't a case of inexperience or conflicting instructions, The RL which gives Opus its fantastic ability to just knock out features is the same RL which causes it to constantly accumulate tech debt through short-sighted decisions.