Up- and downvoting appears to be borked on this instance specifically. If I hit the buttons, they light up, my upvote is counted - and a split second later it disappears and the button greys out again.

If I reload the page sometimes the vote got counted in the background, sometimes it didn't.

This appears to affect other parts of the UI as well. Most of the time I expand an image, it expands for a split second, then the UI resets and the image is small again.