DNS resolver cache stale after vendor failover

Your payment vendor posts a status update at 14:00: their primary endpoint had an outage and they failed over by repointing api.vendor.com to a new IP set ~15 minutes ago; they say traffic should be recovering. But your checkout error rate stays pinned at ~40% timeouts to the vendor for another 25 minutes even though they're 'back.' Dashboards: a subset of your app pods recovered immediately, while others keep dialing the OLD IPs and timing out. dig api.vendor.com from a fresh pod returns the new IPs; the stuck pods' in-process resolver cache still holds the old ones. The vendor's DNS record carries a 3600s TTL. How do you triage and mitigate?