Cross Platform Sharing

One of my kids ONLY plays Fortnite on Switch. In the past, he’s bought the V-Bucks cards, redeemed it using my phone and then bought whatever packs/skins on the Switch

Yesterday he bought a card, and did the above, but when he logged into the Switch, his v-bucks total was different than what was on the phone account

Contacted Epic for support and they said “the v-bucks are not missing, they are on the child’s epic games account. The way cross sharing platform works means they’re not visible on the Nintendo platform”

Is this a new thing they’ve introduced??