@Banxix I've been able to suppress the error by doing the following:
Editing /Banxix/AutoCloseThreads/XF/Entity/Thread.php line 56 with:
PHP:
else
{
if (isset($entity->post_date)) {
if ($entity->post_date + (\XF::options()->autoCloseThreadsTimeFactorMinutes * 60) < time())
{
$this->threadStateClosed();
}
}
}