Why are running OpenCart pages returning 404?

Question

opencart

There is a store on OpenCart, its pages give a 404 response code, but they are normally visible as if 200. These are category pages:
https://monogramstone.ru/rustovye-ugly-iz-kamnya/
https://monogramstone.ru/navershiya-iz- rakushechnika/
https://monogramstone.ru/pilyastry-iz-rakushechnika/
https://monogramstone.ru/pano-iz-rakushechnika/
https://monogramstone.ru/kolonny/
https://monogramstone.ru/karnizy- iz-rakushechnika/
https://monogramstone.ru/kronshteiny-iz-rakushechnika/
https://monogramstone.ru/arkhitekturnye-nalichniki/
https://monogramstone.ru/zamkovye-kamni-iz-rakushe...
https: //monogramstone.ru/plitka/
https://monogramstone.ru/plitka-interernaya-natura...
https://monogramstone.ru/balyasiny/
How to fix it?