It might not be much help, but have you been able to delete and reinstall the app?
Worst case scenario you could set the TV to factory settings.
This I had to do a few times whenever NOW was playing up especially when I had an active sports membership.
So I don’t have an active sports membership. However I do know what 25fps can cause with sports and that the same channel with 50fps is smooth.
Annoyingly not all sports channels become automatically supported in 50fps with boost.
Whilst I understand your frustration I do because the “picture quality aspects” of Boost SHOULD be in all memberships as standard.
Boost should only be used to get rid of any third party adverts for on demand content.