"Is it working now?" asked the Product Owner. "Well... I hope so. You know this bug, it can not really be reproduced locally, therefore I can not really test if it works now. The best I can do is deploy it to prod and wait."
The answer did not make the Product Owner particularly happy, but he also knew the bug appears only when an API called by his application has a quick downtime exactly at the time when the user clicks on a specific button.