Threads are missing from the timeline

[MadLittleMods]

Steps to reproduce

1. As UserA, create a room
2. Send 10x messages, start a thread on the 10th message add 2x thread replies
   • Repeat this 5 times
3. Add some messages on the end for good measure
4. As UserB, join the room
5. Notice all of the threads are missing
6. Click on the threads list and notice how all of the threads magically appear now

Outcome

What did you expect?

Threads are visible in the timeline from the beginning.

Why doesn't Element show the thread preview based on the bundled aggregation/relations of the message? But also clearly, Element paginated over where the thread replies should be anyway. What happened to them?

Message "40" event source

{
  "content": {
    "body": "40",
    "msgtype": "m.text",
    "org.matrix.msc1767.text": "40"
  },
  "origin_server_ts": 1671166588638,
  "room_id": "!jKOotgfiQODgEnlHkJ:matrix.org",
  "sender": "@erictroupetester:matrix.org",
  "type": "m.room.message",
  "unsigned": {
    "age": 571239,
    "m.relations": {
      "m.thread": {
        "latest_event": {
          "content": {
            "body": "40 thread reply2",
            "m.relates_to": {
              "event_id": "$Mhu-FIe1fF2mfdwgeISxzmMekf_zRybOvlfbhj2yDw4",
              "is_falling_back": true,
              "m.in_reply_to": {
                "event_id": "$sapwxdnkg_H5FWK7cWJIPqcWQ0zCc5QMPNyXBqkWvW0"
              },
              "rel_type": "m.thread"
            },
            "msgtype": "m.text",
            "org.matrix.msc1767.text": "40 thread reply2"
          },
          "origin_server_ts": 1671166598660,
          "room_id": "!jKOotgfiQODgEnlHkJ:matrix.org",
          "sender": "@erictroupetester:matrix.org",
          "type": "m.room.message",
          "unsigned": {
            "age": 561217
          },
          "event_id": "$FHtruJ4cdNW437XzkoHI9LxgSsY-_fmtjrpFmzf2nyc",
          "user_id": "@erictroupetester:matrix.org",
          "age": 561217
        },
        "count": 2,
        "current_user_participated": false
      }
    }
  },
  "event_id": "$Mhu-FIe1fF2mfdwgeISxzmMekf_zRybOvlfbhj2yDw4",
  "user_id": "@erictroupetester:matrix.org",
  "age": 571239
}

Additionally, threads should be shown regardless of how far away the thread reply was sent from the thread root. But this doesn't even apply to this case as the thread replies are sent immediately after the thread root.

What happened instead?

The threads are missing

chrome_2022-12-15_23-00-16.mp4

Operating system

Windows 10

Browser information

Chrome Version 108.0.5359.99

URL for webapp

https://develop.element.io/

Application version

Element version: a7124c9-react-b728b2743565-js-447319737a05 Olm version: 3.2.12

Tested with v1.11.15, v1.11.16, and latest develop.element.io where it's all reproducible

Homeserver

matrix.org

Will you send logs?

No