It's confusing but Shopify keeps this for 30 days. This means that your app hasn't faced problems for 18 days and it's OK.
If there was a problem it would have updated the "Last detected" days.
It's written in their docs
After you remove the deprecated calls from an app, the app's status stays as Fix by (date) until 30 days after the last deprecated call was made. The time of the last deprecated call is shown below the status indicator on the Apps page of the Partner Dashboard.