Temperature could certainly explain this. I open my pool on the early side and have been timing the weather pretty well (getting dumb lucky) the last few years and hitting an early warm spell soon after opening. I considered the notion for a brief instant that CYA might be heavy and thus wallowing in the hopper until fully mixed, but the bottom drain was a nagging source of doubt, then came my Graduate School Dean, a chemist, who said CYA is no different in suspension than milk in your coffee.