Would seem LG TV's simply don't have sufficient internal memory to run these apps. Support is frankly useless and the only solution is to return the set for a full refund as no fit for purpose or put up with this. IMHO the sets are overpriced, have only average sound even through LG soundbar, flacky WebOS and standard definition broadcast TV is below average quality of picture. HD is slightly better and 4k video, when you can find it, nothing special either. Would not recommend or buy LG again.
November: YouTube app for WebOS was updated but sadly the 'This app will now restart to free up memory...' error, which has been reported for over three years, continues to plague these poor TV's so I assume LG & Google are incapable of fixing the issue or simply don't care and LG certainly are not going to refund all their customers conned into buying this rubbish let alone send engineers round to install adequate hardware.