Recently, I hit a nasty bug while using a library that was new to me: characters were disappearing while typing in an input form on Android.
The LLM had access to the library's source code and docs but couldn't figure it out. Same with their own AI chat on the docs.
I found on GitHub issues that this bug had been fixed with a new flag when instantiating the library.
This new flag, added because of the bug, is not documented as fixing this specific problem.
It's only mentioned in a post in the ticket's issues.
After finding that the issue was solved, I tried web searches. Sometimes the bug shows up, sometimes it doesn't.
If it had been documented in the source code, the LLM would have found it with no effort.
Great documentation is still the cornerstone of great developer experience.