How old is your LG TV, and is it running webOS?
The older sets 2014 and earlier with Netcast will shortly no longer run the NowTV app, as support for this old version is withdrawn.
But if it is a webOS set, delete the app, unplug the TV at the mains, wait two minutes, plug it back in, reload the app from the Store, and try again.
OK, sorry then, but that was my best shot.
So it looks like the LG update ‘hard broke’ NowTV - and not just NowTV, if All4 got broken too.
In which case, you need to report this to LG; either for them to fix it, or for them to point out the failures in the NowTV and All4 apps to their respective developers, for them to fix.