Portfolio Nav: prev and next not showing

https://the-raw-canvas.com/work/have-a-nice-day-nlzlm

On the above link, the previous and next navigation is not visible on some pages. I'm unable to edit that section and I've used the global color pallet. Any ideas?

Because pagination text is white color. You can change its color in Design > Site Styles or add this to Design > Custom CSS

h2.item-pagination-title {
    color: white !important;
}

If some other pages you need black color, you can edit have a nice day page > Add a Code Block > Paste this code to change title to white

<style>
  h2.item-pagination-title {
    color: white !important;
}
</style>