Hmmm. Things are getting complicated!
The ITV Hub (per se) app doesn't appear to be supported on Panasonic TVs:
https://help.itv.com/hc/en-us/articles/115000562353-Which-Connected-TV-devices-are-supported-
However ITV Hub is also available through the Freeview Play app, which is what I suspect that you've got on your TV. It appears that there's something wrong with the app, so that it might need updating or reinstalling. Unfortunately I've not got a clue as to how you'd go about doing that but I know who should be able to assist you and that's Panasonic UK Support. Give them a call on 0344 844 3899 to see if they can help. (Calls are charged at the same rate as 01 and 02 numbers are, on both landlines and mobiles. If you've got spare 'included minutes' in your phone package, that will mean that the call is free of charge).