How to fix forward to next post(s) within same gallery

Hi Piotr, we've followed a previous support to have the buttons at the end of each posts to go back to main gallery and forward to next post(s) within the same gallery. The problem is that works now on some galleries and not in others, also on the last post if you click forward to next post instead of restarting like for GK NSP Grid sends you to the next gallery page/post...

-Fix forward to next post (within same gallery): <?php next_post_link(); ?>

That's what we've found with you. But what and were we should edit to change it correctly thru all site posts?

Thank you in advance,
Andrea

Hi,
Could you send me a PM with your website URL?