could be a few things, since no one can see what you are seeing.
most likely your paralax isnt set properly or all the way, and its actually paralax swim.
My daughter's 6.5-20x50 LRT had this. It held up two seasons and then went to shit in a match. Was shifting back and fourth from the X ring to the 7 rings in a 1 minute wind condition. We send it in and Leupold said they adjusted parallax. I haven't reinstalled it. She got a hold of one of my NXSs and won't give it up.
keep an eye on it. May be nothing, but I would test it often until you are sure it's gonna hold up.