If you are using PrestaShop 1.7.8.4, please update the version to PrestaShop 1.7.8.5. Version 1.7.8.4 has critical hook issue which prevents features like Layout Type, Overriding etc.
See the link : https://build.prestashop.com/news/prestashop-1-7-8-5-maintenance-release/
Please Update PrestaShop 1.7.8.4 to PrestaShop 1.7.8.5