Hi @mark, this is a long-standing known issue.
Per the documentation of the clientKey field:
Identifying key for the Atlassian product instance that the app was installed into. This will never change for a given instance, and is unique across all Atlassian product tenants. This value should be used to key tenant details in your app. The one time the clientKey can change is when a backup taken from a different instance is restored onto the instance. Determining the contract between the instance and app in this situation is tracked by AC-1528 in the Connect backlog.