Magento 2.2.6 - Attribute with ID "Manufacturer" does not exist

I ran into this problem as well. Possibly due to a module we installed, the attribute was created and deleted. What ended up working to run the upgrade, was to create the attribute in the database. With the following queries.

INSERT INTO `eav_attribute` (`attribute_id`, `entity_type_id`, `attribute_code`, `attribute_model`, `backend_model`, `backend_type`, `backend_table`, `frontend_model`, `frontend_input`, `frontend_label`, `frontend_class`, `source_model`, `is_required`, `is_user_defined`, `default_value`, `is_unique`, `note`) VALUES (NULL, '4', 'manufacturer', NULL, NULL, 'varchar', NULL, NULL, 'text', 'Manufacturer', 'validate-length maximum-length-255', NULL, '0', '0', NULL, '0', NULL);

INSERT INTO catalog_eav_attribute (attribute_id, is_global, is_visible, is_searchable, is_filterable, is_comparable, is_visible_on_front, is_html_allowed_on_front, is_used_for_price_rules, is_filterable_in_search, used_in_product_listing, used_for_sort_by, apply_to, is_visible_in_advanced_search, position, is_wysiwyg_enabled, is_used_for_promo_rules, is_required_in_admin_store, is_used_in_grid, is_visible_in_grid, is_filterable_in_grid, search_weight, additional_data) VALUES (****eav_attribute attribute_id****, 1, 1, 1, 1, 0, 0, 0, 0, 0, 1, 1, "simple, virtual, bundle, downloadable, configurable", 1, 0, 0, 0, 0, 0, 0, 0, 1, NULL);

With that I was able to compile the code. So far I have not come across any issues. But I'm not entirely sure if this is the correct answer to the issue. As I saw in a previous thread it is not a safe to create attributes manually in the database. But nothing ventured, nothing gained.

We posted the same question on github for Magento 2. https://github.com/magento/magento2/issues/18134

I downgraded to 2.2.5 again using composer, used the database from the backup I created before, or just revert to the backup. Create the manufacturer attribute using the specs according to a original/clean 2.2.5 installation for that attribute. Again updated to 2.2.6, and it worked without the error.