It looks like that plugin is possibly using the single template for the archives so you would need to force it to display correctly by adding this code to ‘Customize’ > ‘Additional CSS’:
.post-type-archive-lp_course .masonry-entry.masonry-2 {
width: auto;
}
.post-type-archive-lp_course .masonry-entry.masonry-2.course {
width: 31.3333%;
}This should fix it in your particular case, but if you change the theme’s blog layout in the future, the code above will also need to be modified.
The Learnpress plugin should be using the archive template for course archives, with the single template only for each single course page. It would be worth asking the Learnpress plugin support if they can fix this issue so that it works properly.