Stubbornly 1-column on attribute archive pages

I’m trying to set my shop to show 3 columns on all shop loop pages. I’m using the following code in my child theme functions.php

add_filter('loop_shop_columns', 'loop_columns', 999);
if (!function_exists('loop_columns')) {
	function loop_columns() {
		return 3; // 3 products per row
	}
}

This successfully results in the following for the main shop and tag archives.

<ul class="products columns-3">

However, on attribute archives, it outputs:

<ul class="products columns-1">

If I click the “customize” button, it magically changes to class=”products columns-3″. If I change themes it gets fixed, too.

Does anyone know where this is getting set? I don’t have any customized woo templates in my child theme.