Order posts alphabetically with numbers but some of the posts has numbers in the title

I have this query:

 $  args = array(        'post_type' => 'alerts',     'post_status' => 'publish',     'posts_per_page' => -1,      'orderby' => 'post_title',      'order' => 'ASC', );  $  alerts_loop = new WP_Query( $  args );  

The problem is that the order breaks in certain point. look at the imagen any ideas why it breaks. I have used:

'orderby' => 'title', 'suppress_filters' => true, 'ignore_sticky_posts' => true 

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