I decided to fix this by setting the pointer-events of the element containing the next/back buttons to none, so the taps can be registered by whatever's behind it. Then I set the pointer-events for the next/back buttons themselves back to auto so that they can be tapped. I made a couple of changes to the content area of the page to try and ensure that the fixed-position navigational buttons don't visually overlap anything in the content area.
I decided to fix this by setting the pointer-events of the element containing the next/back buttons to none, so the taps can be registered by whatever's behind it. Then I set the pointer-events for the next/back buttons themselves back to auto so that they can be tapped. I made a couple of changes to the content area of the page to try and ensure that the fixed-position navigational buttons don't visually overlap anything in the content area.