That sounds slightly different from "here is a question, say I don't know if you don't know the answer" - sounds to me like that was Opus running in a loop, presumably via Claude Code?
I did have one problem (involving SQLite triggers) that I bounced off various LLMs for genuinely a full year before finally getting to an understanding that it wasn't solvable! https://github.com/simonw/sqlite-chronicle/issues/7
It wasn't in a loop really, it was more "I have this issue" "OK I know exactly why, wait" $3 later "it's still there" "OK I know exactly why, it's a different reason, wait", repeat until $35 is gone and I quit.
I would have much appreciated if it could throw its hands up and say it doesn't know.