I've notice the juice gets really fouled vaping it in cold weather, not to mention if it's a bottom coil it will cause leakage when it warms up. It tastes great when I'm out in the cold but then when the juice warms up, the flavor becomes muted and it burns the nose. I just dumped a few ml out of a protank for that very reason as a matter of fact. Thought it would get back to normal in time but it never did. My hypothesis is that since the different ingredients freeze or at least thicken at different temperatures, they get separated when your tank gets very cold. So when you're vaping in the cold, you might be vaping just the pg or just the vg, leaving other ingredients frozen, especially if the vg is thinned with water. When it thaws out, your juice has less vg or pg now and more percentage of water or whatever parts of the ingredients didn't get vaped away in the cold, leaving a nasty tasting combination. That's my theory anyway.