My simple custom shortcode is not longer working (possibly due to upgrade to WordPress 4.4 ?)

I have a simple function in functions.php that creates a custom shortcode:

function my_line_break() {
    return "<br>";
}
add_shortcode( 'new line', 'my_line_break' );

Now, I don’t know if this happened after upgrading to 4.4 but it’s not longer working and pages just render [new line] in plain text.

Anyone can help with this?
I looked at https://make.wordpress.org/core/2015/07/23/changes-to-the-shortcode-api/ but I’m not sure it relates?

P.S. I know this wouldn’t be the right way to handle line breaks, but I did it as a way to make life simpler for my customer (so as a little side question, if there is a valid and simple to use alternative, could you please let me know it so I can also bypass this problem completely?).

Solutions Collecting From Web of "My simple custom shortcode is not longer working (possibly due to upgrade to WordPress 4.4 ?)"

Converting the comment to an answer,

please rename your Shortcode to not contain spaces (new_line):

function my_line_break() {
    return "<br>";
}
add_shortcode( 'new_line', 'my_line_break' );

Your shortcode name is incorrect . Shortcode API – WordPress Codex

So you can write like :

function my_line_break() {
    return "<br>";
}
add_shortcode( 'newline', 'my_line_break' );

Then :

[newline]