Update: It tuned out that the hinge itself was working fine, so lubing the latch externally didn't do anything. The issue was with the motorized actuator module, which contains a couple of plastic gears and a spring to spin the gear back to its initial position after the motor opens the lock. The spring wasn't rotating the gear back into position because the gear wasn't turning very well.
I took everything apart. There was dirt mixed in with the white factory grease. I cleaned it and applied WD40 Silicone lube, which didn't work that well. Then Liquid Wrench white lithium grease, which worked better, and was maybe what was used from the factory. I also had to be mindful of how much I tightened one of the screws connecting the motor module to the hinge, as too much pressure would warp the plastic housing and prevent the gear from spinning well. It all works for now, at -10C.
In the future I'll use WD40 silicone spray for the hinge, which is very light and shouldn't attract dirt. It's rated for -70C or something. I'll definitely use white lithium or some type of grease for the plastic gears if I have to take the actuator apart again. I'm thinking maybe I should have used a "low temperature" lithium grease, but we'll see how this stuff does when it gets colder.