«Argument 1 passed to Magento\Catalog\Block\Adminhtml\Product\Edit\Tab\ChildTab::setTab() must implement interface Magento\Backend\Block\Widget\Tab\TabInterface, instance of Magento\Framework\DataObject given» while opening a simple product in admin

The error is for simple products only.
There is not error while opening virtual or configurable products.

The bug is related to Admin Product Page is broken: «Element with ID ‘catalog.product.edit.tab.downloadable.links’ already exists»

See the code:

$group->getAttributeGroupCode() can return null.

I opened the eav_attribute_group table and saw that some records has null in attribute_group_code column:

SELECT * FROM  `eav_attribute_group` WHERE attribute_set_id IN (
	SELECT attribute_set_id FROM eav_attribute_set WHERE entity_type_id =4
)

This is because of the incorrect attribute group identifier generation algorithm:
Attribute group code generation algorithm is incorrect because it can return null for an attribute group with non-Latin name

$group->getAttributeGroupCode() becomes the tab identifier. So we have a tab with null identifier.

$childTab->getParentTab() === $parentTab->getId() compares null with null and returns true.

The fix is the same as for 48.

How to add tab to product page? I can not use event as magento 1.x. can you help me. Thanks

How does your question related to the topic?

I know that my question is not related in the topic. But because I’m trying add custom tab to edit product page. If you have some ideas help me. I will be grateful about that. Thanks.

One topic - one question.