We too have this issue. None of the suggestions regarding inline attenuation, software updates or resetting will have any bearing here because it is a drop-off with the LG platform (and a major one at that).
As far as those who are considering trying for a refund, there are essentially two options:-
If the set was ordered online then exercise your 30 day right to reject.
If past this point then there is scope for arguing it's either unfit for purpose, not of merchantable quality or, as-is perhaps more likely, reasonably expecting the set be used with such services i.e. the set is meant to work with Freeview[HD] services . There is more than one way to skin this cat... ๐ตSee: Consumer rights with Martin Lewis
The problem won't get fixed until LG, and perhaps Freeview et al get their heads together.
To get their attention please up-vote this Facebook post on LG's official page: LG Official Facebook page - Invalid service on WebOS TV
Hope this helps. ๐