I've noticed while hunting, when the temps get into the 20°s I loose spark off my frizzens on at least 2 of my Flinters.
I was thinking the lube in your lock is too thick and slowly done your hammer in the colder temps
Clean and LIGHTLY lube w better oil
Probably a lot of truth in the lubricant getting stiff or thicker in cold weather slowing things down.
Following are two examples with modern guns.
1. Many years ago a buddy used WD40 on a center fire rifle bolt. At 4° F, firing pin didn't fall. Had to heat gun over the defroster on the dashboard of the truck to loosen things up. Note to self, NEVER USE WD40 TO LUBRICATE A MECHANISM.
2. BIL was visiting from up north and wanted me look at one of his handguns (think something designed around 1911) that was giving problems, particularly in some recent cold weather. One look, and to me the cause was obvious, but while the BIL is good with electronics, it’s not a good idea to hand him a hammer or wrench, or let him use a power tool. The gun looked like it was lubed with old axle grease salvaged from an old 1950s Chevy. With the gun unloaded, we placed in the freezer for a few hours. Upon removal from the freezer, he COULD NOT rack the slide no matter how hard he tried until the thing warmed up. After a tear down and proper cleaning with solvent and an assist from an ultrasonic cleaner, the gun was lightly lubed with high/low temperature rated grease and oil. It functioned fine after another round in the freezer. Waiting to hear back next time he takes it out in cold weather up north.
If you are not a believer, take the lock off your gun, put it in the freezer for a few hours, then see how it works when you test it immediately after taking out of the freezer (still off the gun). Be prepared to completely disassemble lock after the freezer test as it will frost up like snow cone when exposed to the warm air outside the freezer.