Twitter Widget does not show

Hi,

for some reason the plugin does not show if I run it as a widget in the sidebar (simple child-theme twenty-fifteen). In fact, the output of the site just stops with outputting the heading of the widget. That is, the widget area shows the search field and the categories (which are listed before the widget), but the rest of the page remains blank. Also the debug-output of the plugin does not show at all.

Works perfectly fine if I include the plugin as a widget directly in a post (debug output looks unsuspicious).

WP version is 4.4.

Any thoughts…?

https://wordpress.org/plugins/wd-twitter-feed/