I've got a similar problem, which appeard a couple of days ago. I can't choose 'reference style' anymore. And yes, the Zotero app is open while i'm trying to use it in addition to Word
@AndersD it is always better to create a new thread if you are not sure that your problem is exactly the same as the one described in an existing thread.
We will need more details, see https://www.zotero.org/support/reporting_problems