[MarketPress eCommerce] MarketPress - upgrade to 3.2.8 - problem with checkout mini-cart

Upgrading from Marketpress 2.9.6 to 3.2.8
WordPress 4.9.7
PHP 7.1.10
I have disabled all other plugins.

During checkout, clicking 'View Cart' in the floating mini cart just reloads the page. Checking the 'View Cart' element, I can see the href is not defined:

<a class="mp_button mp_button-mini-cart" href="">View Cart</a>

Debugging the includes/common/template-functions.php code, in function mp_store_page_url() the call to mp_get_setting( $page has value 'checkout':wink: is returning null for the $post_id so therefore it returns a blank href value.

if ( $post_id = mp_get_setting( "pages->{$page}" ) ) {

So how is this mp setting actually set? I've already tried re-saving all the Store Settings pages and I don't know what to try next.