In Strategy 10.x and 2019, opening the Warehouse Catalog in Developer causes the error, "Unexpected Error. 'Text' property is read-only" to appear.

The reason this error appears is because an unused database instance is dependent on a database connection that has been deleted. This dependency causes the Warehouse Catalog not to open because the database connection no longer exists in the metadata.
To successfully open the Warehouse Catalog, delete the unused database instances in the metadata.