Try This Code
use Magento\Framework\App\Action\HttpPostActionInterface as HttpPostActionInterface;
class Save extends \Magento\Catalog\Controller\Adminhtml\Product\Set implements ...
For Magento 2.3.4 you can use this:
public function __construct(
$this->collectionFactory = $collectionFactory;
public function something()
Had the same issue and in my case it was caused by a product import with a third party extension.
As a completion to @Fabian the solution that I found is to find all the bundle products that are problematic and save them manually from admin panel. This is a solution when you do not have a large number of bundle products, otherwise maybe a script that will ...