hook_commerce_order_presave firing on page load
This is unusual. The hook should not be executed on every page load. You might want to check if some code in a custom module, custom theme, rule is causing an update of commerce_order which could trigger the hook.

To ensure that the order is updated on every page load, you can implement hook_entity_update(), in your custom module

function MODULE_entity_update($entity, $type) {
  if ($type == 'commerce_order') {
    // Execute your code here.
  }
}


If the code inside if loop is still executed, you can be sure that the something is triggering update of commerce order on each page load. And you can proceed to find out what is the actual cause of the problem.