Customers are reporting to partners that they are unable to uninstall apps after a cancelled subsrciption ands appears to be linked to their billing cycle. There is a known knowledge article already on this, so it is a known issue, however it appears to be a breaking change.

KB: [Can't uninstall apps after cancellation | Jira | Atlassian Documentation|https://confluence.atlassian.com/jirakb/can-t-uninstall-apps-after-cancellation-1369277736.html]

You can review the latest CDAC thread here: Please allow app uninstall for cancelled subscriptions

There is more documentation reinforcing that this is the "intentional" design...
Apps: why uninstall button is disabled?
How can I uninstall an app before the end of the trial period?