Ok I have discovered that problem is in getSpecificPrice function in classes/specificprice.php
You have to replace SQL select. So:
Not working select:
$query = '
SELECT *, '.SpecificPrice::_getScoreQuery($id_product, $id_shop, $id_currency, $id_country, $id_group, $id_customer).'
FROM `'._DB_PREFIX_.'specific_price`
WHERE
`id_shop` '.self::formatIntInQuery(0, $id_shop).' AND
`id_currency` '.self::formatIntInQuery(0, $id_currency).' AND
`id_country` '.self::formatIntInQuery(0, $id_country).' AND
`id_group` '.self::formatIntInQuery(0, $id_group).' '.$query_extra.'
AND IF(`from_quantity` > 1, `from_quantity`, 0) <= ';
working select:
$now = date('Y-m-d H:i:00');
$query = '
SELECT *, '.SpecificPrice::_getScoreQuery($id_product, $id_shop, $id_currency, $id_country, $id_group, $id_customer).'
FROM `'._DB_PREFIX_.'specific_price` USE INDEX (id_product_2)
WHERE `id_product` IN (0, '.(int)$id_product.')
AND `id_product_attribute` IN (0, '.(int)$id_product_attribute.')
AND `id_shop` IN (0, '.(int)$id_shop.')
AND `id_currency` IN (0, '.(int)$id_currency.')
AND `id_country` IN (0, '.(int)$id_country.')
AND `id_group` IN (0, '.(int)$id_group.')
AND `id_customer` IN (0, '.(int)$id_customer.')
AND
(
(`from` = \'0000-00-00 00:00:00\' OR \''.$now.'\' >= `from`)
AND
(`to` = \'0000-00-00 00:00:00\' OR \''.$now.'\' <= `to`)
)
AND id_cart IN (0, '.(int)$id_cart.')
AND IF(`from_quantity` > 1, `from_quantity`, 0) <= ';