Unless someone put pressure on the panel (maybe by wiping it?) I don't see how this could develop overnight. Sometimes you don't notice things that get gradually worse until it hits a certain point, and once you've noticed it you always see it.
Is it normal? Well, in my experience corner flashlighting is not uncommon in edge-lit sets. Even brand new it can be fairly bad. Yours might be a little worse than the ones I've briefly owned.
You could try calling LG, but they may say that some bleed is endemic to the tech and not do anything.