My Chase Card stopped charging interest !?

I have a Chase credit card that's been carrying a balance on a promotional rate from the early 2000's. It was one of those obsolete, "3.99% Until Paid in Full." When Chase tried a few years later to change those terms and end the promo rate early (which they later got sued for under a class action), I also closed the account to prevent their change from going into effect. Since then, I've continued paying the minimum payment due each month for 20+ years. The balance is now about $260, and the minimum payment is now $10 (which I think was the lowest minimum allowed on the credit agreement from back then which is still in effect). So I now expect to finally pay off this closed credit card account in another 2 years in 2028, as long as they continue waiving the interest.

With that all said, something strange has happened. From Sept., 2025, they stopped charging the 3.99% interest! The credit card bills show the promotional rate in effect with the average balance of $260, yet the finance charge at the right is $0! Any idea why, after 20 years, they've stopped charging interest? Never read something like that in a credit card agreement!