GP has no control over where the Auto Ads are placed. This is all down to Googles code as it randomly chooses where to add the code. And sometimes this is inside the sticky navigation which creates the problem you’re having.
Option in GP – Disable the Sticky Navigation. At least if the advert is added inside the navigation you’re users will be able to scroll.
Options outside of GP – check your AutoAds configuration to see if there is a setting to remove it from that location – OR replace auto Ads with standard Ad Units.