Override core/gallery block

Hello,

I did override the core block for the gallery using in my functions.php file :

<?php
function my_register_gallery() {
        unregister_block_type('core/gallery');
        register_block_type( 'core/gallery', array(
                'render_callback' => 'my_gallery_render',
        ) );
}
add_action( 'init', 'my_register_gallery', 10 , 1  );

It was perfectly working, but since a few days (I did the last update of wordpress 5.8.1), and maybe a little bit before, but I am not totally sure, I have an issue:

If I use the unregister_block_type function I cannot override it with register_block_type and the block disappear in the editor. And a strange thing occurs, I have this message on the former existing gallery blocks :

Your site doesn’t include support for the THRON block. You can try installing the block, convert it to a Custom HTML block, or remove it entirely.

If I don’t use unregister_block_type('core/gallery'); before, I have this message :

Notice: WP_Block_Type_Registry::register was called incorrectly. Block type "core/gallery" is already registered. Please see Debugging in WordPress for more information. (This message was added in version 5.0.0.) in /Users/the_user/wordpress_folder/wp-includes/functions.php on line 5663

All of that was working before with no alert.
I tried with all my plugins deactivated, and with removing all my function.php files actions.