The menu I use on my side panel is longer than a standard screen height so a reader would have to scroll the see the entire menu.
On android phones the side panel scrolls correctly - the side panel and the content scroll together.
On iPhones, the content side scrolls independently and the side panel scrolls until mid way through the menu only.
My side panel options are set as such:
Enable Slide Out Panel - enabled
Panel width - 85%
Toggle Bar Text - Posts by category
Animate panel - no enabled
Animation duration - 150ms
On my desktop site, I'm using a Graphene child theme. (in case that has any effect)