Post and reply module malfunctioning after update

Hi, 

After updating the plugin to the latest version, the writing module no longer gives feedback after a successful reply.

It just stays stuck on the page and shows a brief black and red notification box without text. I'm using the UM theme. See screenshot. This screenshot is taken after pressing submit reply. 

The reply does show up after refreshing the page. The module is gone at that point. 

Any ideas what I should be looking at? I tested in both Firefox on desktop and Safari on iOS