actually you are correct.

i am running a module that is overriding the bestseller list; and is using an older version of the module.

the change did happen in v158a, and specifically this commit:

https://github.com/zencart/zencart/c...980bee4b28f972

the old code was like this:

PHP Code:
  $rows = 0;
  while (!$best_sellers->EOF) {
    $rows++;
    $bestsellers_list[$rows]['id'] = $best_sellers->fields['products_id'];
... 
the index value being the var $rows, and here, it starts at 1.

the new code is like this:

PHP Code:
    $bestsellers_list = [];
    foreach ($best_sellers as $bestseller) {
        $best_products_id = $bestseller['products_id'];
        $bestsellers_list[] = [
            'id' => $best_products_id,
            'name'  => $bestseller['products_name'],
... 
with no explicit setting of the index, it will definitely start at 0.

good catch.

as to what is the most eloquent way to address this error, i can not say.

but the commit i referenced above is definitely where this bug got introduced.