This.
Your 100 yard zero is your zero. It should basically never change. I'm pretty sure the environmentals would have to be staggeringly different to produce a "click" worth of POI change at 100 yards. For instance I tried it out with my hunting rifle's ballistics (assuming a 50 yard zero just to see if your temp difference would change my 100 yard drop), and it didn't change the 100 yard drop at all.
1. Something got bumped and shifted your zero, could be one of these.
- Scope itself lost zero. What scope do you have on it?
- Scope rings slipped. What rings do you use?
- Scope base is loose. Have you loctited your scope base screws if the scope base is not integral?
- Barreled action shifted in the stock. What stock is it and is it bedded? Same questions if it's a chassis.
2. Your POI is changing because of drastically different management of the rifle, prone vs bench sort of thing.