Description

I simulated a conversation between two users in a thread. When a user sees the other party message, it will send a read receipt

POST https://matrix-client.matrix.org/_matrix/client/r0/rooms/[ROOM_ID]/receipt/m.read/[EVENT_ID]

With a body

{ "thread_id": THREAD_ROOT_ID }

When this is processed, the other user will receive the m.receipt event down /sync. However I notice that the thread_id that has been passed in the original request body is missing (highlighted in red below).

{
  "type": "m.receipt",
  "content": {
    "[EVENT_ID]": {
      "m.read": {
        "@germaingermain:matrix.org": {
          "ts": 1668591503180
-         "thread_id": THREAD_ROOT_ID
        }
      }
    }
  }
}

Steps to reproduce

• Send a read receipt from one client
• Inspect the sync response of the other party

The issue does not occur when the two users are using the threads dev server we have for internal testing.
However the issue seems to happen on matrix.org/element.io, I am unsure whether this happens only over federation or not

Homeserver

matrix.org

Synapse Version

1.71.0rc2

Installation Method

No response

Platform

n/a

Relevant log output

n/a

Anything else that would be useful to know?

No response