I searched for hours, sadly no luck. I deleted every billing_contact one by one in the quote module php files, with various effects, however the field always filled (except when it was no longer present at all).
With more research I tried to populate it by adding the following to the viewdefs.php in the quotes module, however its not working either.
Thanks for the guidance!
array (
'name' => 'billing_contact',
'studio' => 'visible',
'label' => 'LBL_billing_contact',
'displayParams' => array (
'field_to_name_array' => array(
'id'=>'billing_contact_id',
'name' => 'billing_contact',
'primary_address_street' => 'billing_address_street',
),
),
),