The brand I am using is Inland. I've used 20+kg of this brand and I would say that it is mostly good. That was why I wondered if it might be in the machine.
I contacted the manufacturer and they don't think there's a problem so maybe its just a maintenance thing. Another 3D printer with a lot of experience told me that he changes the Teflon guide every 5kg. I think I'll try that, and buy a different brand.