add_theme_support misbehaving

Edit: (see my answer lower- still not quite fixed)
I can get the gallery shortcode working well with my plugins with a fresh roots theme but not with my updated roots theme.
I made sure those are set up though:

add_theme_support('bootstrap-gallery');

require_once locate_template('/lib/gallery.php');

And… I pasted the gallery.php once again in its place just to make sure.

It’s giving me the <dl> gallery that I imagine Wordpress shoots by default.

Any idea what I could be forgetting?

I found the cause, I just had to remove:
if (current_theme_supports('bootstrap-gallery')){}; in gallery.php
but why doesn’t it work even if I have my add_theme support('bootstrap-gallery'); in place. (I moved the add_theme support(); in functions.php by the way which should be ok since wp codex says so.
Another mystery:
The nice-search does not work in the exact same way but for jquery cdn it seems to be just fine.

You need to make sure the theme support settings are set before the lib files are included.

add_theme_support('correct'); // This will work.

require_once locate_template('/lib/correct.php');
require_once locate_template('/lib/wrong.php');

add_theme_support('wrong'); // This will not work.

Indeed. Thank you Foxaii.