Disconnect the Netgear Orbi, and only connect the BT YouView box to the BT Home hub, and see if the problem goes away.
Thie issue would be that the Orbi is interfering with the multicast stream from the home hub.
If the Orbi has an IGMP snoooping option, the enable it, and that should prevent it from interfering.
I assume the Orbi connects to one port of the BT Home hub, and BT YouView connects to another port?
By the way, when using the Orbi on its own in router mode I am using the standard BT open reach modem which gives really great stable internet connection
If you are connecting the YouView box to Orbi, it very unlikely it has the bandwidth available to maintain a consistent video stream over its wireless mesh system. I don`t think the BT Whole Home system works either.
Using it in AP mode with the home hub, it should be possible to implement parental controls, similar to what the BT Whole Home system has.