What part of the country are you in? I never had issues with mine separating and it goes from near freezing to near 100 in my garage throughout the year, but temperature shift throughout a single day is less than 10F typically.
If it's not a freezing issue, i'd guess it was daily fluctuations in temperature.
I bought it from AG last July. I'm in South Carolina and this winter we might have gotten a few nights around 20F and not in a row. All of my other gallons are fine (Simple Green, Purple Power, MG Wheel Brightener). I'll give them a call and see what they think.