Perhaps this is not the case. The first message shows that you created a field for a specific post. If you are trying to access this field from another template, then you need to use additionally the id of this post.
in post <h4>Somme text: <?php the_field('custom_filed'); ?></h4>
outside this post <h4>Somme text: <?php the_field('custom_filed', $post_id); ?></h4>
e.g. <h4>Somme text: <?php the_field('custom_filed', 10); ?></h4> where 10 is ID of post
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