The get() will cause an exception, when there is no entry for this specific supplier in the s_articles_supplier_attributes table. You should add an IF-Statement like this:
{if $supplier.attributes.core}
{$supplier.attributes.core->get('attribute')}
{/if}
There might be some old installations that are missing the entries, because this functionality was added with 5.2. You cann add an entry for every supplier via sql to fix this.