BaseElementExtension.php

<?php

namespace App\Extensions;

class BaseElementExtension extends Extension
{
    /**
     * Flag to indiciate if this element is a new element. Used because isChanged('ID') seems to be unreliable
     *
     * @var bool
     */
    protected $isNewElement = false;
    
    public function onBeforeWrite(): void
    {
        if (!$this->owner->ID) {
            $this->setIsNewElement(true);
        }
    }

    /**
     * @param $bool
     */
    public function setIsNewElement($bool): void
    {
        $this->isNewElement = true;
    }

    /**
     * @return bool
     */
    public function getIsNewElement(): bool
    {
        return $this->isNewElement;
    }
}

elements.yml

---
Name: app-elements
---
DNADesign\Elemental\Models\BaseElement:
  extensions:
    - App\Extensions\BaseElementExtension
SilverStripe\Core\Injector\Injector:
  DNADesign\Elemental\Services\ReorderElements:
    class: App\Services\ReorderElements

ReorderElements.php

<?php

namespace App\Services;

use DNADesign\Elemental\Services\ReorderElements as ElementalReorderElements;
use SilverStripe\ORM\DataObject;

class ReorderElements extends ElementalReorderElements
{
    public function reorder($elementToBeAfterID = 0)
    {
        $element = $this->getElement();

        // We want to prevent the default behaviour of re-ordering new elements
        // to be at the start of the list
        if ($element->getIsNewElement() && $elementToBeAfterID == 0) {
            $element->write();
            return null;
        }

        return parent::reorder($elementToBeAfterID);
    }
}