I've been using the Air rifle for fox grinding as to not spook the entire lake, I've noticed that a majority of the time there is a massive inaccuracy issue.
At first I believed it to be an issues with the weapon not holding zero data after switching to another held item, I would switch back and zero again.
After further encounters I've noticed that on some harvest screens I have a 100m perfect broadside angle for lung shot but for some reason the fox will survive and run, once on the harvest screen it shows the pellet hit the ankle or atleast lower than it should have to hit for 100m zero'd shot.
I still subconsciously reapply zero when reequipping the air rifle just to be sure.