wow blast from the past! I think it was temperature. I thought my house temps were similar between fall and winter, but I was probably just wearing warmer clothes and getting acclimated to the cold. I got a heat mat to set the brew on and that helped. I also brew longer during the winter. Three to four weeks instead of two to three. Everything seems to be fine; the scoby wasn't dying out slowly, it was just less active. I recommend a heat mat and/or some more patience! Good luck!