Working with human serum and plasma samples, after separating from formed elements and making aliquots of the sera and plasma, some of them haven't frozen (around 10% of the aliquots, mainly serum) despite being in the freezer throughout the weekend. They're not as liquid as they would be at room temp, but they're not solid either. Has this happened to anyone before? I have to check the freezer's actual temperature, but we've stored samples before and they froze as expected.

Thanks in advance.

Javier.