It's a bit late but I hope this can help someone..
I've had the same problem, I was unable to delete a wishlist... I realized that in themes/name-of-the-theme/js/modules/blockwishlist/js/ajax-wishlist.js the js file wasn't up to date. I took the js file from the module in webroot/blockwishlist/js/ajax-wishlist.js and replace the old js file and it worked fine for me.