This appears to be a known problem with the October release of Sonnet 3.5 and reportedly affects Haiku 3.5 as well. We've tried different prompting techniques but can't stop it consistently, this has also been reported by several users to Anthropic. For now, the most effective solution seems to be switching to a different model.
We will mark this thread as nofix
, as there are no actionable next steps for us. If we have misunderstood anything, please let us know