Have you tried adding some extra boosting or using a bamboo booster instead of hemp? Caty might just be weeing more lately. If the boosters always come out very wet then it could just be a case of adding something for more absorbancy. Sometimes if you over-boost it can cause some leakage because of the thickness but it doesn't sound like the reason in your case.

Are the nappies still the right size? They haven't been through a hot dryer a lot?