Why is drupal spitting out urls like entity:/node-1474 instead of /node-1474
You have to use .url instead of .uri, like this:

{{ item.content['#paragraph'].field_home_slider_button_link.0.url }}


I don’t think this works on older versions of Drupal 8, so if it doesn’t work you can try this:

{{ item.content['#paragraph'].field_home_slider_button_link.0['#url'] }}