How often do you torque your scope rings? When the temperature changes it can cause metal to shrink or expand. The metal on your scope tube is thin & different materials have different rates of thermal expansion, your rings may be aluminum, steel, maybe magnesium this can cause a variance. This paired with normal bumps or vibrations a rifle & optic is subjected to riding in the truck or being in the field can loosen things over time. Every time you zero you should check torque prior. If you are hunting it might not be a bad idea to let that scope acclimate for a while before throwing it in your truck and torque it down before you hit the road. It could mean the difference between a great shot and a “how in the hell did I miss that” Same if you are traveling to a big match.
There are a lot of great torque wrenches out there which can fit nicely into your range or hunting bag. Vortex makes a nice torque screwdriver and Fix It Sticks are great kits you can even use with drivers most of us have laying around the house.