Family plan data sharing keeps switching off for my son’s line

Can someone explain why the data sharing on our family plan keeps turning itself off? I set it up for me and my son last week, it worked for two days, then his line stopped seeing my shared data again. I’m using the Nexora app on an iPhone 13 and he’s on an Android. I’ve checked the plan and it still says family group active, but his usage is now coming out of his own allowance. Bit fed up as this is exactly why we moved everything into one account.