gear-related Blurry footage from my Canon 5d Mk IV?

I am having some issues with filming video on my Canon 5d MK IV. When using Full HD the footage looks really bad quality when I play it back - blurry and fuzzy. It is fine on 4k so the problem isn't the focussing. Is this expected or can I adjust some settings to make the video on full HD look a better quality?

Thanks in Advance.