I clicked "Approve" for statement ID 7560244 (subject Q3298662 Property:P1346 object Q3608161) and got a tiny red window (class="mw-notification-area") saying "notification-failed". Clicking the window dismissed it, but the spinner that replaced the approve button.
There are a couple of problems with this:
the error notification is in a different part of the screen than the users gaze, potentially a long way away the spinner isn't dismissed (which also makes the notification easier to miss)
Reference : https://phabricator.wikimedia.org/T148155