After installing this new version this problem appeared. It didn’t existed in LibreOffice 5.0.4. The only plug-in I have is Zotero and I am on Linux/Ubuntu.
(sorry, I still don’t have enough points to post the image)
(edit: activated screenshot)
Possibly GTK3 issue. So little info means little response.
Updated:
Look at Q64348 for a possible fix.