Messages don't appear until unread indicator "unread messages" is clicked

As reported on gitter, a lot of people have been experiencing a problem lately wherein some messages do not appear automatically.

The unread indicator("x unread" badge) appears, but the messages are not in the chat view (scrolling has no effect). You can also see the messages if you navigate away and come back. Often this is limited to specific people: meaning that you will see some new messages, but not all, which can be quite confusing (e.g., you see one side of a conversation).

---

This seems to be happening when messages are sent from next/staging

The following warning is in devtools console, see public/js/components/unread-items-client.js#L633

An unread item does not exist in the chat collection: id=xxx

Here is the datadog dashboard for missing unreads. Perhaps we should add an PagerDuty alert, https://app.datadoghq.com/dash/101761/situation-room-feb-2016-missing-chat-items?live=true&page=0&is_auto=false&from_ts=1523067384576&to_ts=1525659384576&tile_size=m

AFAICT, we never get a websocket frame for the new message so I assume it is a problem with the server pushing down the new message

---

As a note, chat-cache is disabled (known to cause issues), http://next.gitter.im/