Several years ago I bought one of those tabletop butane stoves like they use in resturants figuring it would be helpful at a picnic table. It works fine in the summer but as it gets cooler it's hard to get much of a flame out of it. If I have a warm cartridge it works fine for a while.
Years ago we filled a 20# tank down in Florida at Easter time. As we headed home and the temperature dropped I had a difficult time keeping appliances running. Switching to another tank solved the problem. The next summer the FL tank worked fine in the warmer temps. The propane folks explained that they used more butane down south and that was the problem in the cold.
I'm no expert but that makes sense to me. My backpacking stoves use a propane blend to help in the cold too.
Where was your tank filled?
Happy flames, Bigfoot Dave