I've found with sonnet that the longer its output the less it adheres to the prompt. Ask it to write something and not sound robotic and it's exceptional up to

I've found with sonnet that the longer its output the less it adheres to the prompt. Ask it to write something and not sound robotic and it's exceptional up to 1000 words. Then it starts becoming more and more robotic. At 3500 words every last paragraph starts "Remember,...", etc