Jobs & Experts and Marketpress plugin products not in order

Hi

We have a products page on our site where we list all of the credits people can purchase brought in by the shortcode [mp_list_products paginate="1" order_by="price" order="ASC" category="je-credits" list_view="0" filters="0" filters="0"]. A few days ago it worked perfectly how we wanted but has suddenly stopped ordering. If we try ordering by name etc it works perfectly but by price it seems random.

Here is a link to the page so you can see the randomly ordered credits, if you refresh the order will probably change. https://www.pooletogether.co.uk/store/products/
Do you have any idea how we can fix the product orders?

Regards
Matt