Please replace with for increased clarity:

$section = isset($meta['section']) ? $meta['section'] : '';
$page_name = isset($meta['name']) ? $meta['name'] : '_Auto: ' . $template;
$files[$template]['sort_key'] = $section . '||' . $page_name;

Code worked before as well, but since we only have 2 parts to combine, then using implode doesn't really help.

replace / with .

typo

Please:

1. rename sortCompare into compareSMSTemplates
2. rename $a into $sms_template_a
3. rename $b into $sms_template_b

1. name of the method doesn't really tell what it does and why
2. too short variable names
3. too short variable names

replace with:

return strcmp($sms_template_a['sort_key'], $sms_template_b['sort_key']);

there is dedicated function for binary-safe string comparison

1. don't add $section . '||', when $section is empty
2. wrap with substr_count(..., '||')

Sorting by category path gives nothing because categories with large depth, but the short name would be created first. Instead, we should create parent categories first and only then sub-categories.

Bring back the previous code version.