Family Screentime activity not showing on parent's device

Me: iPhone 16 pro max iOS 18.3.2, family organizer

Son (13 years old): iPhone 12 pro max iOS 18.3.2, family member

My son is correctly added to my family, but when going to Family | his name | Screen Time, I don't see any of his activity. It just says "Updating..." below "See All App & Website Activity". This has never worked since creating his account. I've followed these guides (Set up Family Sharing - Apple Support Use parental controls on your child’s iPhone or iPad – Apple Support (UK)) and I've spoken with about 15 different Apple customer support phone agents (including seniors ones), who have taken me through multiple steps, but with no success yet.

Any thoughts on how to fix this?