Had the same problem, LG support were useless only advising TV's are not like smart phones so customers who purchased them thinking the smart TV features would actually work were mistaken so there!
Anyway after trying all the 'fixes' people suggested such as turning off Quick Start and other 'features' and finding this made no difference I saw another solution a member found. This member like me had both Ethernet and WiFi connections enabled and by turning off the WiFi everywhere it is enabled this fixed the YouTube restarting error. I tried this and it has worked for me as well, no more annoying YouTube restarting errors - so far!
Now if I can just get this pile of doo doo TV to stop reformatting my recording hard drive I might have an OK set.