I'm confused about this question, after passed my PSM1 I'd clear that warranty period is over because you have a DoD that determines the minimum level that your code has to pass and PO validates this uses for the potential deliver.
if a bug is detected in PROD, I think that it's a issue has to be resolved by scrum team in the framework of continuous performing of the product, not thinking in a "warrany period" as waterfall methodology because de DoD ensures that the story is ready and without errors for production.
I would emphatize this section about Scrum Guide:
