Causes for vastly different results?

Hubby and I started keto 3 weeks ago & eat the same meals (both working from home).  He is allowed slightly higher macros, but has stayed under 30 net carbs every day, often under 25.  Urine keto sticks have shown I've been in ketosis since week 1 and lost 3kg, where his have have NEVER shown ketosis at all and he hasnt lost any weight!  Could someone take nearly 4 weeks to get into ketosis?  Is there anything else he can do?