I find sonnet and haiku will do that, but I rarely get that with opus. When it does happen it’s a good cue to start a new session. That’s another benefit of the style guide is it’s a good canary for when the model has gone off the rails. If it’s left the style guide, the rest of the response can likely be discarded as departed from reality.
Me: "The gap, stated plainly:" stop using the type of language.
Claude: "You're right. That's one of the constructions your preferences told me to drop, and I used it anyway."