Hi,
I have a similar problem with my Panasonic TV. I emailed their helpline and this was the reply I got.
Quote:
The ITV Hub app is designed to keep viewers signed in.
Could you try resetting the app to see if that resolves the issue for you:
Open the ITV Hub app
On the homescreen press the following on the TV remote: 0 0 0 0 7 7 7
Close the app
Reopen and try again
When I went to try this the Hub signed me in automatically as it should so I couldn’t try it. Maybe it will help you?
Dave