In my v15 instance a manual purchase order works fine. But automated ones, like MTO or manual/automated replenishments ... the dropship address field shows up. so cannot confirm the PO without filling that field out.

This seems to be the related code:

<field name="dest_address_id" groups="stock.group_stock_multi_locations" attrs="{'invisible': [('default_location_dest_id_usage', '!=', 'customer')], 'required': [('default_location_dest_id_usage', '=', 'customer')]}"/>

I have no clue why this should show up ?