Hi,

When only lowercase letters are used, the post cannot be published.

For example, when using the following filter and adding a new post, the back-end and front-end of the site will be stuck. I have to restart the server to recover the site.

add_filter( 'random_post_name_choices', 'hoge' );
function hoge(){
    return 'abcdefghijkmnpqrstuvwxyz';
}

Please check this issue.

Thanks.