I normally have to have a summer and a winter load with ANY powder regardless of "extreme' or not. And it seems that when temps are nearing 80 degrees, all sorts of weird pressure irregularities can occur with pre-loaded ammo. Just how long you leave a loaded round in your chamber when the barrel is warm and the air temp is warming up can affect your combustion. And there ain't no magical powder coating or marketing hype that can change that.
Also, the list the AJ provided is good to look at. I would also add that cases that are different in headspace length due to dies that aren't really full length sizing can change pressures too.
And there are chronos that don't work as well as others and could be affected by muzzle blast, partly cloudy days, weak batteries, and so on.
If it's not far, it's boring.