Categories-option not displayed on Product-page in Catalogue of backend after migration M 1.7.0.3 -> M 2.1.3

[TechNix66]

Today I migrated the content from webshop A to B and during the migration proces of the data I had the following errors:
[2016-12-30 12:24:21][ERROR]: Source documents are not mapped: ajaxsearch,aw_blog,aw_blog_cat,aw_blog_cat_store,aw_blog_comment,aw_blog_post_cat,aw_blog_store,aw_blog_tags,bgsetting,catalin_seo_attribute_url_key,datafeedmanager_attributes,datafeedmanager_configurations,datafeedmanager_options,grid_newproduct,newproduct,newsladdressimport,permission_block,permission_variable,reviewemail,searchanise_config,searchanise_queue,shipping_matrixrate,watchlog,webwinkelconnect_log,webwinkelconnect_reviews,webwinkelconnect_stats,yotpo_rich_snippets [2016-12-30 12:24:21][ERROR]: Source fields are not mapped. Document: sales_flat_creditmemo. Fields: cod_fee,base_cod_fee,cod_tax_amount,base_cod_tax_amount [2016-12-30 12:24:21][ERROR]: Source fields are not mapped. Document: sales_flat_invoice. Fields: cod_fee,base_cod_fee,cod_tax_amount,base_cod_tax_amount [2016-12-30 12:24:21][ERROR]: Source fields are not mapped. Document: sales_flat_order. Fields: cod_fee,base_cod_fee,cod_fee_invoiced,base_cod_fee_invoiced,cod_tax_amount,base_cod_tax_amount,cod_tax_amount_invoiced,base_cod_tax_amount_invoiced,cod_fee_refunded,base_cod_fee_refunded,cod_tax_amount_refunded,base_cod_tax_amount_refunded,cod_fee_canceled,base_cod_fee_canceled,cod_tax_amount_canceled,base_cod_tax_amount_canceled [2016-12-30 12:24:21][ERROR]: Source fields are not mapped. Document: sales_flat_quote. Fields: cod_fee,base_cod_fee,cod_tax_amount,base_cod_tax_amount [2016-12-30 12:24:21][ERROR]: Source fields are not mapped. Document: sales_flat_quote_address. Fields: cod_fee,base_cod_fee,cod_tax_amount,base_cod_tax_amount

Looking to the affected data I configured the map.xml file to ignore these errors.
After that I was able to run the migration without any problem.
As next step I did a re-indexed and cleaned the cache.
When I go in the backend to Products -> Catalogue and open a Product there is no possiblility to select a Category.
This option is completely missing!
The option is there when I select the option to create a new product.
When I go in the backend to Categories the complete structure of the migrated site is there.
But: when I go to a Product via Products -> Catalogue, open it (no Category-section displayed) and save it: all Category assignements for that product are gone.

I encountered this piece already when I was quite far with rebuilding the site.
After that I started debugging step-by-step end found out that it is already there after a clean migration.

Source: Magento 1.7.0.3
Target: Magento 2.1.3, clean install and no custom theme or extra extension.
Migration tool: https://github.com/magento/data-migration-tool (loaded today 30-12-2016)

[dfelton]

This issue can be corrected manually by going to your product attribute sets immediately post-migration of your "EAV Step" in "data" mode, and dragging category_ids into the product's attribute set. I recommend doing this for every migrated product attribute set if you have more than one.

Please see issue #212 for more details.

[TechNix66]

Thanks a lot @dfelton ! Your feedback was the solution for my problem.