'Double Content type' Error when publishing Workflow (after Site Migration)

I have migrated a SharePoint Online Site Collection (Test site) using ShareGate (without Nintex migration feature) to a fresh Site Collection in the same tenant.

SOURCE: customer.sharepoint.com/sites/SiteCollectionTEST/  => DESTINATION: customer.sharepoint.com/sites/SiteCollectionPROD/

The first time I migrated the site by accident to a subsite:  https://customer.sharepoint.com/sites/SiteCollectionPROD/Site

I then restarted the migration and picked the right destination: https://customer.sharepoint.com/sites/SiteCollectionPROD

After a succesful migration I deleted the original subsite.

I then opened the Workflow designer (on the List in new production site) and imported the workflow as a File.

Saving the workflow works fine, but when I publish the Workflow I get an error:

Error publishing workflow. Er is een dubbel inhoudstype Nintex Task Outcome Content Type gevonden.

This is partly Dutch, It says 'there is a double Content Type found"

When I create a fresh workflow (and add a Task Action) and publish, I get the same error.

I'm guessing this error is caused by the initial 'root to 'root subsite' migration.
Who has an idea to resolve this?

BTW: I have emptied the user and (seconds stage) Site Collection Recycle Bins