Sound like you have got a bit of muck in the ceramic disc, unlike a washer these cannot be changed cheaply.
If it is something soft like a bit of swarf from where the plastic tank was drilled for the new dedicated feed then you may be able to remove the cartridge and clean it. If it was metal swarf or a bit of grit then the ceramic will be damaged so you will need to get a replacement ceramic cartridge.
Hope they do spare parts, thats why I always like a known brand like trevi, lifetime gaurantee on the ceramic discs and any spare you need once out of gaurantee otherwise they just send it free of charge
Jason