In Document Setup when changing unit type from say Inches to Centimetres and either tabbing to the next input box or clicking on an input box the unit type doesn't change until you click OK and then go back into the Document setup. Typing in those input boxes will still show "in" not "cm"
Another option you should have is to be able to sync all or selected inputs instead of having to type in each one, this goes for all affinity apps with bleeds and also margins.