401:[Unauthorized]:Could not find stored client data - atlassian-connect-express

Hello,

When uninstalling then reinstalling my app, the following error occurs:

com.atlassian.plugin.connect.plugin.lifecycle.ConnectAddonInstallRejectedException: Error contacting remote application 401:[Unauthorized]:Could not find stored client data for <client_key>. Is this client registered?

I am on version 6.6.0 of atlassian-connect-express. Installations work fine, it is only when trying to reinstall the app that breaks.

I do not have an /installed route defined, only /uninstalled, which is protected by addon.authenticate().

Any ideas would be greatly appreciated!