Ok, I can't tell you for sure the temperature of the air each time I've tried to lock and unlock my car but why would it work sometimes and not others?
If air contracts when it's cold and expands when it's warm isn't it possible that air in a vacuum system would do the same?
I posted earlier about being frustrated with my hatch lock: I had the tailgate apart, adjusted the actuator "away" to take up any play. I also disconnected and plugged all vacuum to and from the gas cap. Everything seemed to be working fine so I put it back together again~
Now it is working inconsistently.
Any assistance would be appreciated, I have performed a search on this issue but would like to avoid buying a MityVac and tearing apart my doors, etc.

Ambient temperature will have a negligible effect. You're chasing a leak of some sort, somewhere.

Does the function vary depending upon how long the car has been shut down? If there is a leak in the reservoir or points sealing against the reservoir, you will lose vacuum over time.

Good luck,

The only possible effect of weather conditions (temp. & humidity) on vac. system is the expansion and contraction of rubber components, i.e. seals, connectors and diaphrams. The colder and drier the conditions, the less likely are old rubber components to do their job.