PHP Warning After Move To New Host

[HM666]

I'm getting the following warning after moving my websites to a new host when I try to save a template after editing it. The old host was running PHP 5.6, the new one is running PHP 7.2.12.

PHP Warning: sizeof(): Parameter must be an array or an object that implements Countable in ..../includes/class_core.php on line 4224

Here is what is in that part of the file.

	// only called when an object is destroyed, so $this is appropriate
	public function shutdown()
	{
		if (sizeof($this->callbacks))
		{
			foreach ($this->callbacks AS $callback)
			{
				call_user_func($callback);
			}

			unset($this->callbacks);
		}
	}

	public function __wakeup()

I can edit templates but it will not show the edits on the site. Any help would be great.