Rv antifreeze

I winterized with super tech rv and marine intifreeze in early oct. And today went out to camper just to check on it and noticed the little bit of antifreeze that was left in the toilet like instructions told me to do is partially frozen. It was a fairly solid shush. I thought this stuff didn't freeze. I'm confused and worried if it is starting to slush up then what is in doing in the water lines, faucets, and pump where I can't see. Any help would be appreciated.