Thanks for you help!
I think with your help/hint I solved the problem. I originally only set the option to check wordpress posts – no other options were checked. When I tried setting the “check category index”-option too this morning, the plugin seems to get all _posts_ (and category-pages) and is right now processing all pages.
As you considered a hook which is filtering the get_posts-query, I also removed a custom query filter from the theme. Although I can’t find any error in this, the options are all not set to “gallery”, this filter sets posts_per_page to 4 – the number of posts the plugin got:
function minimatica_paged_posts( $query ) {
if( (
( $query->is_home() && 'gallery' == minimatica_get_option( 'homepage_view' ) ) ||
( $query->is_category() && 'gallery' == minimatica_get_option( 'category_view' ) ) ||
( $query->is_tag() && 'gallery' == minimatica_get_option( 'tag_view' ) ) ||
( $query->is_author() && 'gallery' == minimatica_get_option( 'author_view' ) ) ||
( $query->is_archive() && 'gallery' == minimatica_get_option( 'archive_view' ) )
) && ( ! is_single() )
)
$query->set( 'posts_per_page', '4' );
}
endif;
add_filter( 'pre_get_posts', 'minimatica_paged_posts' );