Could be that brake fluid is hydroscopic ie
It attracts moisture not air it could be that people have moisture in there fluid possibly causing tiny ice crystals to form
This could possibly block one of the transfer ports in the system causing brake probs
I have never heard of needing special brake fluid for cold weather
Imagine having to take your car in for a fluid change in the winter months or cars and trucks having brake failures due to the wrong type of fluid ?
Bleed brakes new fluid problem solved minus 7 on Monday on the commute no problems