Why are navigation buttons still appearing?

This is a known issue, the only way I think is to set it so the user cannot review or set the slide to reset to initial state if you don't need to score this slide then the best way (not the easiest) is to rebuild the slide not as a quiz slide

Try changing the "when revisiting" state to "resumed saved state" also make sure no other slides have the default navigation turned on (even if they dont get shown anywhere), you can tell if other slides have the default nav on by the location of your custom nav bar - if its off the bottom of the player (as is in your screenshot) then some slide somewhere has the nav on. Its a bit trial and error but you can get rid of the default nav (even when revisiting)

Thanks to both of you, Phil and Andrew.

I did try changing the revisiting state to each of the options, but with no success.  I went ahead and rebuilt it as a plain content slide and I am forewarned now about this issue!

Andrew - I will be more diligent too in checking for the default nav. Thanks!