Warner Bros and therefore HBO Max bought a company called You.i that built their own React Native Rendering engine for low end OTT devices I don't know if they use that engine for mobile or the native RN engines.

Last I heard their whole ecosystem is now based on this.

But if there's scrolling issues and some others, its likely because they're literally trying to run one codebase across everything including OTT devices.

https://www.youi.tv/