One borked thread won't live load posted comment

I've got a thread on our install behaving weirdly. For some reason, this thread won't show comments after they are posted. Clicking the "post" button gives no feedback and comment is not loaded, but comment is actually posted and is seen on reload. If the user presses post again before reloading, that results in a second copy of the same comment, etc.

This does not happen in any other thread. Only particular thing I can think of about this thread is that it got moved around between groups. This did not start happening until I got the latest updates today.

Client console error shown in attached screenshot.

Any idea what might be happening?