Class not found in AbstractFactory

Today I had some trouble with removing a module on Magento2 and its custom product attributes. After removing the code of Mageplaza_Seo I was not able to edit products, categories or even checkout anymore.

The reason was an attribute called mp_meta_robots which was still pointing to the class \Mageplaza\Seo\Model\Source\Robots. I found the attribute by checking the table eav_attribute as follows.

Removing this via backend or MySQL has fixed the problem.