I wonder what code bunq sends when a card has been frozen and the card is still being charged (e.g. due to a subscription).
do_not_honor doesn't necessarily mean the card is stolen, but it certainly triggers Stripe.
insufficient_funds in my experience looks like a safer one. I have never seen the risk level of my old prepaid card increase due to insufficient funds.
List of codes and explanations: https://tidalcommerce.com/learn/card-decline-codes