For the curious, adblockers can get rid of the annoying pop-ups.
I use all of uBlock origin's annoyance filters and it works for me.
www.instagram.com##body:style(overflow-y:auto!important; max-height:none!important; width:auto!important; position:static!important;)
If you permablock it with the picker the scroller will break. They have something from the modal logic tied into the scrolling logic.
For the curious, adblockers can get rid of the annoying pop-ups.