I just checked one of my sites that was working a few days ago and noticed the following error in the sidebar, where I have two datafeedr sidebar widgets - the search and categories widgets:
Fatal error: Call to undefined method Datafeedr_ShopView::form_tag() in /home/sbanks/public_html/metalyardart.org/wp-content/plugins/datafeedr/datafeedr.php(1793) : eval()'d code on line 13
Also, all other sidebar widgets below this do not show. When I removed the datafeedr widgets the other sidebar widgets reappeared. Added them back - anything below them disappeared.