Sub Zero's b+4 misses off-line as well. Check once told me that is due to a character's body position (i.e., it changes when you backdash with 1+2) and the distance between Sub Zero and his opponent. It has nothing to do with lag.
It hardly if ever misses offline. Online play just makes it that more likely to happen. Actually, online, Sub-Zero's b4 rarely ever hits. I'd say 5% chance online, 95% offline. I've played enough off and online to make these percentages.
b2, 4 , freeze, b4... If what you're saying is correct, wouldn't that combo work everytime online? Not only the b4 part, but the b2 part sometimes goes through your opponent in bad lag. Anyway, after you freeze than do the b4, your opponent is always the same distance from you offline or online.
I think lag just enhances the problem with his b4, and his b2. That or I'm missing something.