troubleshooting

I am having weird issues with a scoped rifle not holding zero (and the non holding happens oddly randomly). The scope is a Vector optics Sentinel 4-16x50E-SF, I bought it as used. I am confident that the issue is not related to the parallax error, the reticle stays dead still once appropriately...

Take a look at the video below. When I use my Hornady OAL gauge to push the bullet up to the lands I hit a good deal of resistance, if I push a little harder the bullet then slides up and stops (at what I assume is the lands). When I pull the bullet out it has these marks all the way around...