I have just been sent a new BT TV box to solve the problem of missing apps. Just set up the new box and they are still missing.
Missing Itv Hub and All4 apps can be due to tuning of the Freeview channels not occurring on the Youview box. Do you have an aerial connected and do youi receive Itv on channel 3 and c4 on channel 4 on the Youview box ?
An aerial and successful tuning to Itv and C4 is needed upon initial setup and after certain box resets. Thereafter the aerial connection is not needed for the Itv Hub and All4 apps.