Due to layered navigation block disabling robots by default…
Solution: https://www.prestashop.com/forums/topic/866411-category-pages-noindex/
Hi, the problem comes from the “Layered navigation block” module. After the update to v2.2.1 something has changed.
To Fix the problem for Prestashop 1.6 go to Modules and Services >> Layered navigation block >> Configure
Scroll down to the CONFIGURATION section and set to YES the “Allow indexing robots….”
This action will change the metatags for all category pages to “indexed, follow”