Thanks for the details, I was able to find the cause.
There was a filter active in the functions.php file in your theme folder, but the actual function was disabled. Line 17 was active:
add_filter('asp_results', 'asp_get_tax_term_children_results', 10, 2);
However the asp_get_tax_term_children_results function did not exist, as it was commented. The filter still got executed by WordPress, returning NULL for the non-existend function, therefore emptying the results array.
I've disabled that line, now it will return results:
//add_filter('asp_results', 'asp_get_tax_term_children_results', 10, 2);
It should return results as normal now.Best,
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