Zoom scopes with 2nd plane focusing (of which most are) typically have a small amount of hysteresis (or figure 8) tracking as the power's changed. That's caused by the two lens groups right in front of the reticule moving back and forth different amounts by two cams their mounts are controlled by.
It's best to use a collimator the check a variable scope for "power tracking" or whatever you want to call it. There's too many variables in shooting groups to detect a 1/4th MOA error. I've used a bench collimator testing several variables for power tracking; most are acceptable for hunting 1/3rd to 2/3rds MOA error, a few are absolutly junk (two Nightforce ones I checked( having greater than 1.5 MOA error) and a few are great with less than 1/3rd MOA error; Leupolds.