Next/Previous Post Links wrong in Sidebar

Hello there

I an developing a site with WordPress, I bought and am using the ‘Timeless’ theme and don’t have any plugins installed. All is fine except I want to add the next and previous post links to my single.php sidebar which uses a custom template. If I add the links in single.php all is good but in the sidebar they point to random wrong posts.

There are only 4 categories and every post in each category is ordered chronologically from 1 to 4. I don’t have any post under more than one category.

It sure has to do with my custom sidebar template but I don’t know how to fix it.

¡Thanks in advance for any help you can give me!