While shooting today in cold and snowy Yosemite, I discovered that the shutter is slow in the freezing cold. About 27 degrees F. I had a CLA done a year ago on my Zeiss Super Ikona IV. I thick the grease in the shutter is too thick for the shutter to work properly
Could be that the CLA didn't involve wide temperature range lubricants.
Proper CLA should guarantee reliability down to at least -10°F.