Category archive, but is_category is false

I’m not sure if this is a bug but there’s something weird going on here. I’ve been struggling to figure out why single_cat_title or wp_title won’t work inside an is_category query inside a functions.php function, then I checked the contents of query variable and turns out is_category is null even if there’s a value for the category name and such.

[comments] =>
    [comment_count] => 0
    [current_comment] => -1
    [comment] =>
    [found_posts] => 2
    [max_num_pages] => 1
    [max_num_comment_pages] => 0
    [is_single] =>
    [is_preview] =>
    [is_page] =>
    [is_archive] =>
    [is_date] =>
    [is_year] =>
    [is_month] =>
    [is_day] =>
    [is_time] =>
    [is_author] =>
    [is_category] =>
    [is_tag] =>
    [is_tax] =>
    [is_search] =>
    [is_feed] =>
    [is_comment_feed] =>
    [is_trackback] =>
    [is_home] =>
    [is_404] => 1
    [is_comments_popup] =>
    [is_admin] =>
    [is_attachment] =>
    [is_singular] =>
    [is_robots] =>
    [is_posts_page] =>
    [is_paged] =>
    [query] => Array
        (
            [category_name] => news
            [taxonomy] => category
            [term] => news
        )

queried_object is also null.

Depending on the category archive I browse, sometimes is_archive is true (1), sometimes it isn’t. Sometimes the body_class also turns up a 404 error.

What could be the possible cause for this? Plugins? Permalinks? All of the above?