This happens to me and my friends ALL the time, especially on the map "FIVE". We have been 40+ (as high as round 68 with 2 people), and it not record anything. Other times it records high score, but not rounds survived. Sometimes it updates 1 out of 4 peoples leader board standings, etc etc. It gets really aggravating playing 8+ hour zombie games for it to not even record on the leader boards! 3arc failed hard when they tried to fix the leader boards when it would update your standings after EVERY game, rather you beat your top score/rounds survived. Now it's hit or miss if it records any game at all.
Hopefully there are some 3arc spies lurking around NGU that will see this, and maybe something will get done, probably just wishful thinking I guess. I'm just tired of taking noob randoms to 40+ having them die 40+ times, only to have THEIR leader board standings update and not mine!
And just to clarify the public/private match MYTH affecting the leader board... it DOES NOT MATTER which one you play, leader boards are updated... when they decide to actually work.