After some modification of categories I get this error on the category page in frontend not admin:
Item (Magento\Catalog\Model\Product\Interceptor) with the same ID "160" already exists.
Magento Version 2.1.6
I hope somone can help, thanks!
You can solve this issue using Delete product with id 160 from your catalog product backend.
Because Product with same name already exist and url rewrite is not possible for same name Product. I have faced this type of issue when i had import product using csv.
If Admin Panel Product page not display grid and display popup at that time you have to delete product id with 160 from Database.
Go to your database,
find catalog_product_entity table and delete entity_id with 160.
Run php bin/magento indexer:reindex command.
If issue solved, click Kudos and Accept as Solution.