The issue is not with Virtuemart. It's with content plugin SP Page Builder.
If there is no article id, the plugin return false, it should return an empty string instead.
The fall back return should also return an empty space.
The error is triggered when you use virtuemart because the content plugins are triggered and there is no 'ID' attibute to the $article being passed. Virtuemart uses virtuemart_product_id instead.
Never the less, change your content plugin with this simple fix. You will save headaches to many customers.
Problem is still occuring on SP Page Builder 5.4.6