I found that in 2.4.5 the tagcloud wasn't showing in the allblogs blog. I fixed it pertty easily.

by changing this in the following file inc/widgets/widgets/_coll_tag_cloud.widget.php

$sql = 'SELECT LOWER(tag_name) AS tag_name, COUNT(DISTINCT itag_itm_ID) AS tag_count
                          FROM T_items__tag INNER JOIN T_items__itemtag ON itag_tag_ID = tag_ID
                                    INNER JOIN T_postcats ON itag_itm_ID = postcat_post_ID
                                    INNER JOIN T_categories ON postcat_cat_ID = cat_ID
                                    INNER JOIN T_items__item ON itag_itm_ID = post_ID
                         WHERE cat_blog_ID = '.$Blog->ID.'
                          AND post_status = "published" AND post_datestart < NOW()
                         GROUP BY tag_name
                         ORDER BY tag_count DESC
                         LIMIT '.$this->disp_params['max_tags'];

to this

if($Blog->ID == theallblogid)
{
            $sql = 'SELECT LOWER(tag_name) AS tag_name, COUNT(DISTINCT itag_itm_ID) AS tag_count
                          FROM T_items__tag INNER JOIN T_items__itemtag ON itag_tag_ID = tag_ID
                                    INNER JOIN T_postcats ON itag_itm_ID = postcat_post_ID
                                    INNER JOIN T_categories ON postcat_cat_ID = cat_ID
                                    INNER JOIN T_items__item ON itag_itm_ID = post_ID
                         WHERE post_status = "published" AND post_datestart < NOW()
                         GROUP BY tag_name
                         ORDER BY tag_count DESC
                         LIMIT '.$this->disp_params['max_tags'];
}
else
{
        $sql = 'SELECT LOWER(tag_name) AS tag_name, COUNT(DISTINCT itag_itm_ID) AS tag_count
                          FROM T_items__tag INNER JOIN T_items__itemtag ON itag_tag_ID = tag_ID
                                    INNER JOIN T_postcats ON itag_itm_ID = postcat_post_ID
                                    INNER JOIN T_categories ON postcat_cat_ID = cat_ID
                                    INNER JOIN T_items__item ON itag_itm_ID = post_ID
                         WHERE cat_blog_ID = '.$Blog->ID.'
                          AND post_status = "published" AND post_datestart < NOW()
                         GROUP BY tag_name
                         ORDER BY tag_count DESC
                         LIMIT '.$this->disp_params['max_tags'];
}

Where I changed theallblogid with our actual id.

See here for the solution http://blogs.lessthandot.com/index.php/WebDev/WebDesignGraphicsStyling/b2evo-and-the-tagcloud